I am a little surprised by all the comments and the negativity. What happened to kindness in this world? If it were me I would want to make things right even if it is not my problem.
First of all-what game are we talking about? Is it super rare or something I am missing? Almost every game can be replaced or found. I would offer to help him find another replacement game and work with him. Sounds like he is bummed and made a mistake. I am not saying to give the game back but try and work something out.
-Might help to know what game it is?