Here are two relevant quotes. If we combine them, I think we can conclude that Satoshi is still out there working on crypto-systems:

June 17, 2010: "The nature of Bitcoin is such that once version 0.1 was released, the core design was set in stone for the rest of its lifetime."

Final post:
Dec. 12, 2010: "There’s more work to do on DoS, but I’m doing a quick build of what I have so far in case it’s needed, before venturing into more complex ideas."

So Satoshi 1) thought bitcoin would become relatively set in its ways and difficult to change (which turned out to be true) and 2) said he was moving into more complex ideas.
 
This makes me believe that Satoshi realized that if he was going to continue making revolutionary technology, he had to leave the bitcoin project. Yet Satoshi was relatively obsessed with cryptocurrency, as we can see from this quote:

June 18, 2010: (I’ve been working on bitcoin’s design) since 2007. At some point I became convinced there was a way to do this without any trust required at all and couldn’t resist to keep thinking about it.


Do you think someone so obsessed with cryptocurrency suddenly left the field altogether? Unlikely. I think those "complex ideas" Satoshi was talking about in 2010 manifested themselves in 2011-2014 blockchain tech projects. In 2010, Satoshi and Gavin and others were talking about BitDNS. Namecoin, the first altcoin, was the result in 2011. Bitmessage, a blockchain based messaging protocol, arose in 2012 (another truly innovative project). "Nicholas van Saberhagen" was working on the Cryptonote protocol in 2012. Now we've got more projects than we can count. I'm willing to bet that Nakamoto contributed to some of them. It's funny to think that Satoshi is probably working on some altcoin/bitcoin 2.0 project right now, but I think it's true.