If the delete was just like recycle bin delete or quick format style delete, then the files are recoverable. Whether or not the file names will be intact is another thing sometimes I've seen, which is odd. Hopefully he hasn't been writing to those disks in the mean time. Sure, though, files have been recovered under several layers of overwriting, but those were grad students doing their thesis work. If that sort of thing was commercial by now, I'd charge loads for it since it's high techy stuff. So, I'd say if he needs that sort of recovery then the files are lost forever because I'm guessing he doesn't have that sort of money.
