I see Daenarys dying a heroic death to save Jon (from Euron, perhaps), probably getting Drogon killed in the effort as well. Jon then kills Euron. The tide turns in the battle and the combined forces of the Lannister army and the Golden Company start to lose.
Cersei escapes and gives the command to Qyburn to blow up King's Landing using wildfire. Arya stops Qyburn from doing it. The Hound then confronts the Man Mountain and kills him. However, the Hound is fatally injured in the process (having fought to a stalemate) and dies in the arms of Arya.
My theory is that Jaime goes back to King's Landing and ends up killing Cersei, which fulfills the prophecy that a valonqar (little brother) of Cersei will kill her. She expects it to be Tyrion, but it actually is her younger twin brother, who will then also become the Queenslayer.
Jon becomes the King, with Sansa becoming the warden of the North. Arya becomes head of the Kingsguard. Tyrion is retained as the hand of the King. The standard of the Onion flies high in Riverrun, while we have a sellsword becoming Lord of Highgarden.