This kind of thing keeps coming up in threads lately. There are programs available that claim to help recover deleted items like pictures. I haven't seen anyone have much luck with them, but might be worth a shot.
If the pictures are indeed deleted from the phone, the best thing your friend can do is STOP USING THE PHONE immediately to save anything. Standard phone calls, texts, etc should be ok, but when you delete something, whether on the computer or one of these devices, all you're actually deleting is the path to that file. The file itself is still saved until it's written over. Basically, the device registers the space that was taken up by those files (the pictures in this case) as free space, even though it's actually still there. However, the more the device is used, the more likely it is to save something over that new "free" space and the pictures will be gone forever.
This is how the FBI and etc often catch people that used a computer to write ransom notes and etc. Even if they delete it, if it's not written over (and in this case, written over more than once), it can still be recovered.
I'd recommend a Google search of android photo recovery software and try your luck there, but as I said, I haven't seen much success with it, so your friend may be out of luck.
If nothing else, this is a good time to get him setup with automatic backup to DropBox, Google+, Microsoft OneDrive, (and the list goes on).
I never worry about my pictures because they auto backup to at least 2 of those. If I remember right, OneDrive backs up whenever I'm on wifi and G+ does the same, but only when I'm charging. That way I'm ALWAYS backed up to one and get backed up to the other over night while I'm on my home wifi network and charging the phone.
Hope that helps a little! Let us know.