I do have a few conditions for it not lasting beyond a decade or two.
1. If GRRM does not finish the series
2. If GRRM does not appoint someone else to finish the story
3. If GRRM dies (Hopefully it'll be in a few decades, so he can keep chugging along)
If that all happens, then the fervor from HOTD and other material will eventually fade into a part of fantasy framework. Good to read, but not fulfilling in the end.
Agreed. Tolkien had a bad situation (in story) with Sauron and armies of orcs and trolls and such, but still the heroes managed to prevail and there was hope with Aragorn and such that they would be able to rebuild the damage and rule wisely. With GRRM's world (and this is not intended as serious, dealbreaker criticism), there will most likely be a speck of hope, but that hope will come after a continent has been ripped to shreds by ice demons and human douches.
Plus, fantasy and stories are escapism. We want to have some realism and logic, but we also want a story with heroes and villains and such. The heroes and villains can and should be grey, but the "protagonists" and land we're supposed to root for in ASOIAF seem so bad now, that it seems death would be a happy thing.
TL;DR, for this section: The end of the story does require more hope that things will get better than before the conflicts started, or else it's just a grimdark, unhopeful story.