One of are admins went nuts and deleted stuff off our site and i would like to restore the site back to the way it was yesterday can this be done and if so how?

I'm having a little problemm with one of my current visited forum. The forum was Up and running Yesterday in the afternoon everything was fine Untill about 9:30 P.M . My friend Contact me as i log on to my computer saying that This forum was Hacked . I know it was Hacked because It has the Same link and The Name was change but still in the place it was advertised on Google the Hacker Deleted everyone and know syaing that the Forum was Deleted for ssome reason when it was hacked. The Hacker is know thhe admin and the creator of the forum is out of contact..What do we do??