Thanks to Lisa (Miss Diddy) for messaging me.

Luckily we didnt have a case of another hacker - the reason the forum went missing is because there is an un-resolved bug in the software - if the most recent post in a forum is deleted it cant be down on the forum summary page and actually stops the entire forum appearing !

Kev - best thing to do is add a dummy post for now and ensure you dont delete that one.