We know Hal Finney was involved with Bitcoin in the early days and we know he died. I think Satoshi and Finney worked together on Bitcoin and when Finney died and Gavin was approached by the government, Satoshi got spooked. The private keys for those coins was recorded, but it was worth a few pennies and they did not bother to keep it, because it was seen as part of a experiment.
The Satoshi millions are lost forever ^smile^
Finney died like in 2014 and Satoshi went silent here in December of 2010 and through email in like April 2011. Gavin said the last email he sent was telling Satoshi that he was speaking to the CIA or something. That could've spooked him. It also could've been the out Satoshi was looking for, everyone will think he was spooked and not rally against him leaving.