I canít speak to the specifics but it is possible and usually easy to recover files from a drive provided that 1) there has not been a lot of files written to the drive since the target files, and 2) that the OS on which the drive is written support this or at least makes this possible.
Were it me, Iíd contact the Cannon tech support for the printer and explain the problem. Ask them how the drive is formatted, and if they know of any tools to recover files. If they donít know (which would not surprise me), then once you know about the OS used for the drive, you can probably find drive recovery tools that will work.
I speculate that youíd probably want to remove the drive from the printer and install it as a non primary drive on a workstation. There are probably specific steps involved for doing this right and I donít know enough about the drive to offer factual procedures. Definitely DO NOT do anything until you've talked with support. This includes making further prints.
My sincere condolences to your friend!! What happened to him amounts to a worst nightmare for all of us, Iím quite sure. Let me know if I can assist further.