I'll actually be helpful.
If he wants all his files back, tell him to not use his hard drive at all. in fact take it out of his computer.
When a computer 'deletes' files, it doesn't actually get rid of them. It just gets rid of the file directories making them essentially invisible. They're not truely gone until another file gets written over that space on the hard drive.
so, with that in mind, it is very much possible to retrieve files on a hard drive that have been erased. One can do it themselves with the proper software, a different computer, and an extra hard drive. Or you could take it in to probably any computer shop, although they may charge a large amount.
hope that helps