Cyrus and hilariousandco u=164822 / hilariousetc u=397737 / hilarious* u=1424594 are the main offenders - randomly deleting post weeks and even months/years later - usually in my own threads that I have started (hence the replies are on topic).
Untrustworthy behaviour especially when they then gloat they have done it.
(and most of the time those posts don't show up in a "post deleted" message either)
@theymos sits back and does nothing to curb their behaviour.
OP: My advice is to archive as you go. Don't rely on any "auto" archiving of your posts, it's always best to archive your own work.