But if he moved even a single millibitcoin out of his wallet I think the market might react with panic in fear that he would sell a lot of coins at once, and so the fear of the value plummeting might cause it to do just that.

So even if he is alive, could he ever reap the benefits of those coins?

Hopefully he mined with different wallets so that he's been able to sell smaller amounts of coins without anyone knowing that it was him.