If not him, then his publisher should at least have something set up to prevent any significant loss like that, so we would be seriously surprised if that rumor turns out to be true. Plus, we would expect Martin to make a comment on the situation pretty fast if that did happen, but he has actually been pretty quiet so far.
This is actually one of the details that seems to annoy his fans the most, and the lack of communication between Martin and his community is likely only going to make the situation more and more difficult for him as time goes by.
It looks like for most people, the main problem is not so much that the book is being delayed, but that they are being kept in the dark with no updates from the author whatsoever.
And with that in mind, Martin could probably make the whole situation a lot easier on himself if he just came forward and addressed his fans with some explanation. It doesn’t even have to be anything deep and complex, just a simple statement indicating that he’s encountered some trouble, but he’s still determined to finish the book would suffice.
If he continues to stay quiet about the current status of “Winds of Winter”, we suspect that his fans are going to start giving up on waiting sooner or later.