Did he just return to the original world that summoned him? Or maybe not, if those 3 others don't recognize who he is.
I feel bad for Shina, she died for nothing and failed to pass on her magic power to a successor. Not even her desperate last ditch offer of free sex could keep him there. He could've accepted her power, but I guess doing that might bind him to a contract and force him to stay in that world which he didn't like for some reason.