I think the question is "Is (metaphysical) solipsism necessarily true in all possible worlds if it is true in one possible world?"
To me the answer seems to be no, because although one PW could include p-zombies and 1 person, that doesn't mean all worlds do. So I'm not so sure that metaphysical possibilities are trans-world necessary.
To me the answer seems to be no, because although one PW could include p-zombies and 1 person, that doesn't mean all worlds do. So I'm not so sure that metaphysical possibilities are trans-world necessary.