Bitcoin should be forked and Satoshi's 1 million Bitcoin destroyed completely, if he really owns that much.
A sudden withdrawal of of 1 million (or large gradual withdrawals) should be regarded as an attack on Bitcoin.
Or it should be frozen for now until developers are sure no one is going to withdraw the whole thing and crash the market.
Is Bitcoin decentralized or not? What you're talking about is hard-coding censorship into the protocol. That would destroy everything Bitcoin stands for today.
Free markets are free markets. Someday, those coins will probably be moved and sold because they're held on exposed public keys. If someone wants to dump 1 million coins on the market, it's a good thing in the long run. Distribution from one entity to many is healthy for the overall distribution of money supply. It may result in a painful few years for holders, but it's not worth engaging in hard-coded censorship over.