You screw your car up, you fix your car. We've been through this with BOTH kids. Something like this is NOT worth reporting to the insurance company and with a 10 year old car - 100K on the clock, not really worth a lot of out-of-pocket cash either.
If the skin is OK/cosmetically damaged and it's just the clips that are broken, buy them and reuse the skin. It's not hard to do, just a bit fiddly.
If the skin is torn through at the attachment points, get a matching rear bumper skin and install it. The rear bumper is cheap because its usually the front one that gets taken out in an accident.
It's an accident and a rather silly one at that. Between the repair, the scare, and the butt-pealing you gave him, he'll be more careful in the future. Especially after laying on the frozen winter ground fixing his car.
(been there...done that).
angela