Have you considered the possibility of restoring a back-up which might contain the deleted Threads? If you backup on a daily basis, this should be possible. Then you would only loose those threads between the backup time and when you restore the backup.
Just a thought.
Regards,
The main owner of the site came on and luckily he had a backup from the day before, so all the important stuff was restored.
We still can't work out who did it though. I'll look into the proxy unveiler thingy.