He really became rich if he could remember his private key. This is really a bad thing. Many people have encountered this kind of guy and no one seems to be able to recover their bitcoin number. I think this is a solid capital of Bitcoin so it can last forever. 
You can just even save your private key anywhere that you won't forget. smartphones, emails, write it on note, put it on your wallet, and etc. There are many ways that you can save your private key. But this is a sad story.