J.J. Abrams addressed the "purgatory" theory in an interview. ""The purgatory one is a great one, I love that theory — but it isn't what it is. I'd be frustrated if that were the answer I have to say," he said.
So the survivors are not in purgatory and it's not a dream. And producers say there is a logical explanation for everything.
Check it out:
http://abcnews.go.com/2020/Entertainment/story?id=732221&page=1
I don't think it means any guess will get an automatic "no".I'm surprised he commented at all, and would have expected something like, "who knows, maybe, you'll have to watch..."
But when the guy gives a flat out "no, that's not it", I think he means it. People would feel too duped if it turned out to be that after all.
But hey, you're not alone. My sister-in-law still swears they're all dead too!