George R. R. Martin in James Hibberd's book Fire Cannot Kill a Dragon (on the making of Game of Thrones):
(talking about the 2013 meeting with D&D) It wasn't easy for me. I didn't want to give away my books. It's not easy to talk about the end of my books. Every character has a different end. I told them who would be on the Iron Throne, and I told them some big twists like Hodor and "hold the door," and Stannis's decision to burn his daughter. We didn't get to everybody by any means. Especially the minor characters, who may have very different endings.
I believe the books will already be very different from the TV series. For example, compare season 5 and season 6 with the books A Feast for Crows and A Dance with Dragons (two books of which over 90% of the material has not been adapted). They are not at all comparable. The TV series is a very simplified version with far fewer storylines and political/magical elements than in the later books in the series.
First of all, Bran's storyline in the books contains much more magical elements. The Starks in general are all wargs and have wolf dreams. The fantasy element is rather minimized in the TV series (with the intention of making the TV series more mainstream). In the books, however, that will clearly play more of a larger role and magic will be decisive in defeating the Others (there is no Night King in the books, and George has already made it clear that there will be notable differences in that domain). If Bran will have a leadership role at the end, it will be more likely due to his paranormal abilities as a greenseer. I rather think that Bran will become a kind of god-like figure in the end rather than king, as in the TV series
Second: It's already been confirmed that Stannis will burn Shireen, but I'm 100% sure it will happen in a completely different context than in the TV series. Shireen is now in Castle Black, which is in complete chaos after Jon Snow was murdered for violating the political neutrality of the Night's Watch (interfering in game of thrones by supporting Stannis and collaborating with Melissandre). Stannis is in a village near Winterfell and his position is much more favorable than in the TV series (the Bolton camp seems to be blundering and has no unity). The distance between Shireen and Stannis is now very large, so her burning is not obvious. Stannis would have to conquer Winterfell first (which is very likely in the books) to be in close proximity to Shireen again. Sacrificing Shireen will probably be related to the Others.
It is very unlikely in the books that Cersei will ever sit on the Iron Throne. Her character is merged in the TV series with the so-called Aegon Targaryen, son of Elia Martell and Rheagar Targaryen and half-brother of Jon Snow. In the books, Cersei is a very narcissistic (Trump-like) character who is not popular even with the Lannisters. With her poor governance as Regent of Tommen, appointing incompetent butt-kicking co-governors - she is now infamous throughout the Seven Kingdoms. Such weak governance has paved the way for Aegon - who has now conquered Storm's End (one of the most important castles in the Realm). Aegon has the support of the Golden Company (with elephants!) and the likely support of Dorne (via Arianne) and some "friends in The Reach" (Tarly/Rowan?). Varys and Illyrio seem to be having a lot of success at the moment with their "pawn" Aegon (whose Targaryen identity is in doubt, possibly he is a Blackfyre).
George R. R. Marin has hinted at a succession war between two Targaryens in the next two books, a Second
Dance of Dragons. The obvious choice is a war between Daenerys I and Aegon VI (A cloth dragon swayed on poles amidst a cheering crowd). That works better anyway than a war between Cersei and Daenerys as in the TV series. Unlike Cersei, Aegon would be loved by the people. In the books, there is a very clear build up to the bad image the people will have about Daenerys usurping their beloved king. Daenerys in the books has an alliance with the Greyjoys coming up (with Victarion and Euron Greyjoy) - who do not have a good reputation. Tyrion will soon be at her side (but unlike in the TV series, he is a manipulative Walter White-like personality. Tyrion is also known as kingslayer and kinslayer). The North will not appreciate it should Daenerys pardon Jorah Mormont (a pedophilic, criminal slave trader). The Dothraki and the Unsullied will not be welcomed with open arms in Westeros.
In the TV series, Daenerys is called "an evil personality" out of the blue. In the books, I believe that Daenerys still has good intentions and her heart is in the right place, but that her actions against Aegon will be considered monstrous by the people because he will be so loved.
These are my conclusions based on the last two books released and the preview chapters of The Winds of Winter. There will be a lot of differences between the books and the TV series - that has been clear since season 5. The simplification and deletion of many storylines from the books has the natural consequence that the TV series will have a very different final conclusion. That's the butterfly effect.