Originally posted by PonderableNot a good idea.
If threads "vanish for a reason" there should be an expiration date on them or in the FAQ. Maybe the threads could just be autodeleted after that time. This would guarantee fresh threads all around.
But I'll go for a "after-a-year-with-no-further-postings-the-thread-can-be-closed-but-still-visible" kind of idea in order to prevent unnecessary bumping.