I agree that his pace of telling the story slowed down very much in books 7-9, but for me, book 10 was already a start in taking quite some plotlines to the end.
He disease head nothing to do with this though, since he only was diagnosed with amyloidosis *after* book 11 was published.
About the end of WoT - there has been indeed a lot of speculation during the series about how long it would take to come to an end, but in recent years, RJ declared that he would finish the whole story in book 12, with maybe some very minor plotlines being told in a sequel book, but none which are relevant for the main story.
Not too long ago, he told his wife Harriet and cousin Wilson the complete storyline of how everything would end. He apparently spent a few hours telling this, so it's not just some hints and notes I think. So I guess, although it still might take quite a while, that the final book will be published someday. It's very sad though that it won't be from his own hand anymore...
