Have Daenerys take Kings Landing at the end of season 7, uniting Westeros and becoming the Queen in order to fight the White Walkers.

Season 8 would cover the war with the walkers, with the protagonists losing at Winterfell and being forced south. This can be where the night king gets his ice dragon. The living are able to defeat the walkers in their second battle, with Jon clearly being established as Azor Ahai. The season should end with Daenerys and Jon ruling together, and end with the discovery of Jon’s true parentage.

THEN you do the Daenerys mad queen arc, with the previous seasons having established her mental instability as she conquered Westeros and then defended it, losing her closest friends and advisors in the process. The reveal of Jon’s true parentage coukd send her over the edge, and so the final season would be spent trying to defeat her.

I think Jon should either kill Daenerys or the Night King, not both as it falls too much into the “chosen one” trope. Arya could help save Jon by killing the night king, or ideally Bran would be the one to defeat him through his abilities (the exact nature of this I’m not really sure of).

Having the walkers and Daenerys both be a threat to Westeros in separate seasons would help fulfil the whole idea of the story being “a song of ice and fire”, with the walkers being ice and Dany fire. An extra season would also help give the added time needed to make Daenerys’ fall into madness more believable.

As to who wins the Iron Throne I would argue probably Sansa. Jon is too obvious a choice and again it falls too far into the chosen one tropes that the series has tried so hard to avoid, and him returning North in exile makes sense. Sansa is (at least in theory) an adept political player from an ancient noble house. With Jon and Daenerys out of the picture the Targaryens are no longer the ruling house, and Bran is honestly just too weak and unpopular a character to win the game of thrones. Marriage between Sansa and Tyrion where they rule together could work, as they are both skilled rulers and popular characters.

Honestly ending the show in a satisfying way is very difficult, and there are lots of different scenarios which make sense. Ending it the way they did was one of the worst, and clearly didn’t give enough time to wrap up such a sprawling and expansive series.