Here’s my prediction.
The Night King & Snow Zombies win. Bran is either involved or becomes the new Night King. A remnant of humans retreat to islands - Iron Islands maybe or more southern islands. The Night King & Snow Zombies have their civilization. (Remember Not our universe! - a GRR Martin universe!). Their civilization runs it’s course. They dread or have uncomfortable misgivings regarding the coming of Spring\Summer. (Summer is coming! Arrgh!) It comes, the cycle begins again.
Thus Martin continues his theme of the rise & fall of civilizations. His loose parallel with Global Warming continues. (Martin remember is a liberal. It would not surprise me that somehow he blames his universe’s humans for the cycle!) Right now his Ice Age style cycle where its just part of their universe seems to me where’s he’s going with the story. So many Starks, many Lannisters, many Tagaryons, etc. This story is one cycle! I think this explanation fits what I see in his style of story telling.
If the Knight King and his dead zombies win; there will be no future. They will simply go back into hibernation and go dormant. Surviving humans should have future because the zombies can’t cross water without a ship. Of course all it would take is the Knight King and a few dead zombies to cross to the Iron Islands on one ship then every new dead person would rise as a Knight King zombie until all living humans were eventually eliminated.
Just thinking out loud...