Satoshi will return, its been foretold:

https://bitcointalk.org/index.php?topic=1221334.msg12803522#msg12803522

Compare with where this "sullen" quote came from (and the context in which it lives in the story): https://bitcointalk.org/index.php?topic=1186115.msg12486035#msg12486035

FYI -  just for fun on this one, no theories.