Try restarting the phone. If they are still on the device, it may just have not shown until reboot.
If, however, he is backing them up to another device (computer, cloud account, etc.) then he may well have 'moved' them rather than 'copying' them. This would make them no longer on the phone. If that is the case, you would need to get him to copy them back over to the phone.
Now if they were deleted and/or you for some reason can't ask for copies back, that is another story.
While there is no guaranty that you can get them back. Deleted does mean deleted. There are a few apps/programs out there that 'may' be able to help you recover the data.
A few of the programs you could try would be... DiskDigger, MobiSaver, Android-Recovery and...