[deleted] means the original author removed the comment. Comments killed by the mods are marked [dead] and are normally invisible, only showing up with the showdead option on in your profile enabled.

It's bad manners to delete a comment that already has a reply, but we don't prevent people from doing it.

It wouldn't be fair of us to delete the repliers' comments just because a parent no longer exists. That's up to each replier.