Winds of Winter has literally nothing to do with the strike because it's a book. He's perfectly okay to write for Elden Ring 2, for that matter.
If anything, the strike should be good news for the people who still care about asoiaf because now George can't spend all his time writing five different pilots for the various projects that are all going to get cancelled or promote his tv shows on conventions.
That's not how this works at all. I honestly don't know how to explain to you that tv shows and books are different things without sounding like an extremely condescending asshole, so I won't even try.
The strike rules come from the union, not from the greedy capitalists trying to fuck over the writers. There's absolutely no reason for union to have a rule forbidding people from writing books. Especially since HBO can't even adapt the book into the TV show, anyway. GoT is over, they're not going to reboot season 5 or 6 or 7 or 8 to show us the WoW adaptation.