Do not think you can delete FaceTime, could be wrong. But look and make sure he didn't add it to another folder? Go to the search on ipad enter word FaceTime and see if it pops up, if it does you still have it
Go to Settings/General/Reset/Reset Homescreen Layout. That will bring it out of hiding.
As mentioned it cannot be deleted since its a native app. Hopefully he didn't get rid of it by using Restrictions. If so, you'd better hope he remembered the password.