Yes, I've had an old safe with mechanical lock fail on me. Luckily (sort of), the safe was open when it failed so after my boss ditched me (Fri evening, safe wouldn't close and lock) saying, "we'll get you some time off next week if you have to stay the weekend," I was motivated to pull the inner panel covering the lock, look at it and disassemble/reassemble the locking mechanism. Tested it with the drawer open and it worked like a champ so I stored the files and locked it up.

I've seen safes with the locks fail while closed -- that's a real pain in the butt.