I'd say the chances of him getting anything back is about 0%. It is definitely an expensive learning mistake though...
Should he file a Police report on this? He has not done so yet. Is there a chance the stranger could get nabbed when he goes to cash in at an exchange?
It depends on which country. However, it is most likely that the Police will not able to do anything about it. I think I would personally give it a try though.
Considering how much money it is, I would also try and find out who this "stranger" is. It should be possible if they met in person as you described. Perhaps someone at the local bar knows the guy.