Just to point out that any potential recovery process is much smoother, and likely to have a positive outcome, if you can sign a bitcoin message or pgp message from an address you might have written on the forum at some point (ideally, in an unedited post, or quoted by somebody else).

The hacker may or may not have gone through prior posting history to deleted these addresses, but there is also the off-chance that it may have be quoted by somebody else.

If posts have been edited by the hacker, you may (slim chance though) find some archived posts using tools such as TheWayBackMachine, which may have captures a snapshot of something relevant at some point in time.