I'm pretty sure nothing would happen if he stopped paying.

I don't think civil debts can be enforced over international borders.

I could be wrong, and he would almost certainly either not be allowed back to the US or be chased by an army of legbreakers when he gets there, but I don't think a lot will happen otherwise.

Also, did the pickup driver's insurance not foot the bill?
(Flap Burger hasn't really got a burger made of flaps, Tue 16 Mar 2010, 16:03, 1 reply)

A quick Google brought up
"If there is no such [reciprocal] agreement in place, a creditor can sell a debt to an agency in the relevant country and debt recovery procedures will commence under the law of that land."
(Iggy Pop's Teeth, Wed 17 Mar 2010, 12:38, closed)