I had a couple of comments under my answer (this one), and was about to reply to a comment of the question author when I noticed that the author had accepted the answer and deleted his account. Then, after I hit the Add Comment button to submit the reply, I noticed that all the comments vanished.
Why remove the comments so early? Was it assumed that the OP won't ever return to the post to read the reply? Or were the comments somehow deleted automatically when the OP's account was deleted?