The protocol would only be in trouble if the code was changed in negative way, node operators allowed him to sway them, or followed a fork. I think it wouldn't matter but there is none zero chance it would go poorly.

kepford

bitcoin

If Satoshi Returned

If he did return I think the protocol would be in trouble now ud have a head to cut off and if he started schilling etc could see alot of people abandon the network as a whole and just go about their lives probably take the sovereign route acquire some land and live peacefully not much would change just cut bitcoin out n go back to bartering and maybe some metals 