I made a comment to an answer, which resulted in a follow up comment after which I edited my question and the answer on which I commented became obsolete and was deleted. The answerer undeleted his answer to create a new answer, and my comment, now thoroughly irrelevant, reappeared with the techiyas hameisim of the answer. Is is possible to issue a message to the inbox of someone with a resurrected comment to allow them to re-assess it?
Comments on posts retain their "state" if the post is undeleted -- that is, if the comments were deleted before the post is deleted then they stay dead, but if the post with comments is deleted and later undeleted, the comments are undeleted too. Often this is correct; perhaps the comments address issues in the post that haven't been corrected. There's no way to automatically know which comments are no longer relevant.
If comments come back that are obsolete, please flag them.