Never EVER Sublet

When one of my roomies for next year suggested we sublet to someone over the summer, I thought it'd be a good idea. The subletter is someone we all know, and someone we knew valued personal space and therefore would take good care of the apartment over the summer. UNFORTUNATELY, we've had one problem after another.
First, my former roomie decided to let her boyfriend stay in the apartment after her part of the lease was over, encroaching on my subletting friend's space and time. When we got the boyfriend to move out, I thought, "Good, my problems are over."
NOW, MORE PROBLEMS HAVE SPRUNG UP.
1) The basement key is lost?!! I don't want to have to pay for a lock cutter...?!!
2) My subletting friend has managed to piss off the apartment building people and now if his car is so much as seen in the vicinity of the building, it'll get towed...?!!!

At least former-roomie's-boyfriend was polite enough to return my call as to how to return the apartment keys...