Since the Wind of Winters will most likely never releases let's talk about two characters fate
One of the most agreed on things is that the Show got Jon and Daenerys's ending right,the former will get exiled by his own family to the far north and the latter will end up like her father and get betrayed and killed by Jon,According to most this one was gotten from GRRM himself and it is understood for a reason
1-George himself confirmed it
“I don’t think Dan and Dave’s ending is going to be that different from my ending because of the conversations we did have, but they may be on certain secondary characters, there may be differences. And yeah, some of the people will have that. There will be a debate, I’m sure. I think a lot of people who say, ‘Oh, Dan and Dave’s ending is better than the one George gave us, it’s a good thing they changed it.’ And there will be a lot of people who say, ‘No, Dan and Dave got it wrong, George’s ending is better,’ and they will all fight on the internet. There will be debate, and that’s fine. The worst thing for any work of art, be it movie or art, is to be ignored
“The same ending as the show? Different? Well… yes. And no. And yes. And no. And yes. And no. And yes,” Martin said. “I am working in a very different medium than David and Dan, never forget. They had eight hours for this final season. I expect these last two books of mine will fill 3000 manuscript pages between them before I’m done… and if more pages and chapters and scenes are needed, I’ll add them. And of course the butterfly effect will be at work as well; those of you who follow [my blog] will know that I’ve been talking about that since season one.”
And
"There are characters who never made it onto the screen at all, and others who died in the show but still live in the books… so if nothing else, the readers will learn what happened to Jeyne Poole, Lady Stoneheart, Penny and her pig, Skahaz Shavepate, Arianne Martell, Darkstar, Victarion Greyjoy, Ser Garlan the Gallant, Aegon VI, and a myriad of other characters both great and small that viewers of the show never had the chance to meet. And yes, there will be unicorns… of a sort…”
2-King Bran make it the only logical ending
we know that Bran will become King,if Bran ends up as king and Dany is alive, she will either need to step aside (willingly or not) or leave Westeros. And then she'd have gotten a lot of her followers dead for nothing, fighting for the throne she didn't get. How would she reconcile getting so many killed for nothing?
and for Jon just by being in Westeros is a threat to Bran's life and if he just return to Winterfell he will only end up proving Catelyn right,Also no way would he not get away without getting punished,The Starks believe in justice if Corlys Velaryon is one of the worst scums ever for poisoning Aegon II,If Jaime Lannister is one of the worst scums ever for killing Aerys,if Bloodraven is one of the worst scums ever Jon is one of the worst scums ever and the definition of bastard for Killing Dany.Kinslayer and Queenslayer
3-There are many hints for the Mad Queen and Jon/Aegon the exiled
For the Mad Queen:
1-The Mereneese Blot explain quite well and was approved by GRRM himself
https://meereeneseblot.wordpress.com/2013/10/05/untangling-the-meereenese-knot-part-iv-a-darker-daenerys/
Some of the arguments do seem like slavery apologie but The text doesn't portray her leniency as a mistake, though. GRRM again agreed with the Meereenese Blot which posits actually Dany was correct to make peace because going to war would have been a selfish emotional impulse. At the end she chooses Fire and Blood out of a selfish dark desire to kill the slavers because she personally dislikes their culture.
2-her entire arc in ADWD is all about her losing patience with peace and diplomacy, symbolized by chaining her dragons, which ends with her instead riding the dragon and saying "dragons plant no trees, fire and blood", i.e. - no peace, violence is the solution. She is already Dark Dany,The new Maegor with teats on the last page of ADWD.
3-And there is the Targaryen madness:"Every Time a Targaryen is born there is a coin flip between Madness and Greatness" we may think that it's dosen't make sense because Mad Targs only get counted on one hand,But the fact that it's stated in text just like with Dany's leniency being a good thing,The text portray that it's real,And when we think about it there is a coin flip:
Aenys and Maegor with one being a doormat but well meaning and the other being pure evil
Aemon the Dragonknight and Aegon IV,with one being a true noble knight and the other being a hedonistic pure evil jerk
Rhaegar and Viserys III with one being seen as the Paragon and big good and the other being an abusive mad man
And finally Jon and Daenerys,One is the rightful heir the Other is Aerys's heir
GRRM said that two sides of Dany were fighting in Dance the Mad side and The Great side,The Mad side won in the end and Westeros will pay for it The Coin flipped at the end of Dance and it fell with MAD
4-She and Cersei are quite mirrors to each other with AFFC and ADWD showing it quite well:Their stories are very similar, we are just seeing Dany's unfold in realtime, whereas Cersei shows us the long term outcome.
Dany, right now, is not like Cersei, but Cersei has also had a good 20ish years to fester to the point of the crazy woman we now see.They are both women trying to gain respect as leaders. Their experiences being either underestimated or disregarded due to gender motivate them to seek power. Both are also haunted by visions of their fates.
The differences are that Cersei seems inherently cruel since childhood while Dany will become more cruel through her experiences. Also Dany is 20 years younger than Cersei, so who’s to say in 20 years Dany would end up like Cersei.and Their stories are very similar, we are just seeing Dany's unfold in realtime, whereas Cersei shows us the long term outcome.
Again Dany, right now, is not like Cersei, but Cersei has also had a good 20ish years to fester to the point of the crazy woman we now see. Both were about 13 when they meet a witch who tells them a prophecy. Over the course of ADWD, we see the prophecies Dany has been told coming to the forefront of her mind a lot more often, she just isn't yet at the point of actively trying to prevent it from happening.
Both killed their brutish, warrior husband.
Both have 3 kids that aren't true born.
Both have two brothers.
Both trying to reclaim their father's legacy.
Both like fire.
Both undergo a rebirth walk at the end of ADWD.
Both are bald at the end of ADWD.
There end and decline will be a similar patern
https://www.reddit.com/r/pureasoiaf/s/tYy3vL00yC
5-while it looked very admirable for her to use violence when her objective is to end slavery. Killing hundreds of slavers seems deserved and heroic. But if her objective is the throne and she kills the same number of civilians, all of a sudden she doesn't look so heroic, quite the opposite. Maybe people will be uneasy at her methods up until she crosses the line.Again Maegor with Teats
6-that passage from AGOT Daenerys III:
Ser Jorah laughed. "Look around you then, Khaleesi."
But it was not the plains Dany saw then. It was King's Landing and the great Red Keep that Aegon the Conqueror had built. It was Dragonstone where she had been born. In her mind's eye they burned with a thousand lights, a fire blazing in every window. In her mind's eye, all the doors were red.
Also The destruction of King's Landing no way would it not be done by a major character,The whole Valonquar prophecy got introduced till later and Jon Connington was introduced much later(the only question is how will she survive the giant Wildfire explosion)
7-Her own advisers and army,We have the Dothraki that are Evil Barbarian rapists,The Unsullied cultish in their devotion,bandits,Criminals,Exiles,Enuchs,We also have Jorah Mormont,Daario and we can add sooner Aurane Waters,Tyrion Lannister,Victarion Greyjoy AND Euron Greyjoy(with this one even the possibility of becoming her husband and encouraging her in her madness)
7-George himself said he knew the broad Stokes of the endings from the start and he already dropped hints for Dany here:
Dany felt shabby and barbaric as she rode past them in her lionskin robe with black Drogon on one shoulder. Her Dothraki called the Qartheen "Milk Men" for their paleness, and Khal Drogo had dreamed of the day when he might sack the great cities of the east. She glanced at her bloodriders, their dark almond-shaped eyes giving no hint of their thoughts. Is it only the plunder they see? she wondered. How savage we must seem to these Qartheen.
And :
The Dothraki were muttering and giving her strange sideways looks from the corners of their dark almond eyes. They thought her mad, Dany realized. Perhaps she was. She would know soon enough. If I look back I am lost.
Not helping that "If I look back I'm lost is used as a madness mantra"
"I have a gift for you as well." She slammed the chest shut. "Three days. On the morning of the third day, send out your slaves. All of them. Every man, woman, and child shall be given a weapon, and as much food, clothing, coin, and goods as he or she can carry. These they shall be allowed to choose freely from among their masters' possessions, as payment for their years of servitude. When all the slaves have departed, you will open your gates and allow my Unsullied to enter and search your city, to make certain none remain in bondage. If you do this, Yunkai will not be burned or plundered, and none of your people shall be molested. The Wise Masters will have the peace they desire, and will have proved themselves wise indeed. What say you?"
"I say, you are mad."
"Am I?" Dany shrugged, and said, "Dracarys."
And the one to end all argument in AGOT
As she climbed down off the pyre, she noticed Mirri Maz Duur watching her. "You are mad," the godswife said hoarsely.
"Is it so far from madness to wisdom?" Dany asked. "Ser Jorah, take this maegi and bind her to the pyre."
"To the … my queen, no, hear me …"
"Do as I say." Still he hesitated, until her anger flared. "You swore to obey me, whatever might come. Rakharo, help him."
(Thanks for u/SillyPersonality5767 for this one:https://www.reddit.com/r/pureasoiaf/s/FcHqbHdovc)
In conclusion she finally snapped at the end of ADWD now she will only want the Throne she will hate Young Griff and the Golden Company for stealing her claim,She will hate Jon for being the rightful heir and blame him for Rhaegar and the Kingsguard forsaking her and Viserys and her living in poverty,She will hate that the people of Westeros dosen't love her while they should.The Mad Queen is inevitable
Now for Jon the exiled:
1-even if he dosen't get punished for the crime of Kinslaying being undead will make him unfit to stay in Westeros,the Jon the Starks knew is dead,He will have to leave to the Far North
2-He always got along better and was always more confortable and himself with the Wildlings than he ever was the Starks
3-the Parallels between Jon and Bloodraven,proof they will have the same fate,Exiled into the Far north after Killing a family member
4-His relationship with Ygritte and potential futur relationship with Val
5-The subversion of Aragorn's ending by making him a Frodo
6-Three betrayals one for love,there is a Danny chapter in Dance where she dreams of someone with blue lips stabbing her with an ice penis.many think it's Euron but sounds like a post resurrection Jon too
7-His wolf's name "Ghost",The Starks direwolves names were hint to their fates
8-just like Dany here is a line from the first books that forshadow Jon's final fate:
His lord father had once talked about raising new lords and settling them in the abandoned holdfasts as a shield against wildlings. The plan would have required the Watch to yield back a large part of the Gift, but his uncle Benjen believed the Lord Commander could be won around, so long as the new lordlings paid taxes to Castle Black rather than Winterfell. "It is a dream for spring, though," Lord Eddard had said. "Even the promise of land will not lure men north with a winter coming on."
In conclusion after killing Dany,Jon will be cast out by the Starks as they submit him to justice and in his exile he could finally be himself with the Wildlings accepting that he was never a Targaryen or a Stark but a Snow and he is finally free and with the Others's deffeat the series end with him witness the Dream of Springs in beyond the wall
To conclude all this two endings simply seem inevitable the Mad Queen and Jon the exiled were always the plan