Bitcoin or crypto currencies can not be banned from the entire world, even government of countries ban cryptocurrency and still, the citizens of such countries still go about buying and trading in bitcoins and crypto currencies secretly, so any ban on crypto currencies won't really affect the price much if at all it moves the market.
And again, if the great Satoshi Nakamoto comes on and wants to sell his 1m or 2m bitcoins, I believe he's not that stupid to want to sell everything in one go, he will definitely sell them bit by bit which I don't think will affect the price in anyway, bitcoin has gone really far and not even Satoshi himself can stop it, so whether he sells off all he's holdings, people will always be ready to buy it from him.