After Buddha died, his shadow was still shown for centuries in a cave—a tremendous, gruesome shadow. God is dead; but given the way of man, there may still be caves for thousands of years in which his shadow will be shown. And we—we still have to vanquish his shadow, too.
If you want to add a "supernatural" touch to your campaign, define the rules of magic and the universe. Make your players comfortable with those rules. Then your new supernatural creatures must then break those rules.