In this type of scenario, I dont think I would take it. I would first find someone looking for it and probably send it back to him or just let him know that he should change his wallet already. But I dont understand how can someone get that unless they are really careless and just not thinking about their protection and put a lot of money in. Its not a good idea.
Any thoughts on how you'd find them? (Assuming that all you knew was their key/s and address/es.)