I'm betting the show finishes before he finishes Winds of Winter. And forget seeing A Dream of Spring anytime this decade.
Most likely. I'm thinking HBO will spin off some kind of prequel/sequel set in the Westeros/Essos universe - maybe that's what Arya's line about 'What's west of Westeros?' was all about.
Don't you think it's nearly impossible for GRRM to be a stream of consciousness guy though? Especially writing a book with so many balls in the air? He's gotta' be a writer who plots out the story completely first, and then writes it. Or nearly completely.
In my meh attempts to write, I've always been the former, letting the stories unfold - but I found it daunting to keep two dozen characters straight, let alone thousands.
So my suspicion is that Benioff and Weiss have at the very least had detailed notes/maps/outlines since day 1, and of course the great turtle's phone #.