There is no reason for him to come back. Bitcoin is a decentralized currency. If he comes back, people are going to consider him as a central figure of bitcoin. Anything he does or says will have a huge influence in the bitcoin market. And lets not forget about the FUDs that are going to be spreading when he comes back. I am sure some people will start panic selling because they will think Satoshi might sell his coins. Bitcoin has been developing well for decades without Satoshi. Other than knowing who the creator is, I doubt anything good or new will happen when Satoshi returns.