It doesn't take long to damage once there is no oil in the engine, the residual oil may protect it for a little bit so it is hard to say. At this point if everything is the same as before then chances are it will be fine. If any new and unusual sounds are now present then failure is in his future. Something has been damaged. When I used to train people, never ever leave anything loose, either take it off or tighten it but never leave it loose. One of my pet peeves there, I've seen more techs forget and leave it loose and have oil everywhere.