awwww, i'm so very sad to hear the news
i've been a fan since the early 80's - i still have my original copy of pawn of prophecy - and althalus is probably my favorite, as well.
btw, a lot of the books that didn't list leigh as co-author were still a collaboration between them. i remember reading in the intro of one of the books that dave said that "the secret is out" and that his wife had worked with him since belgariad books.