Ok so:
Percy got Medusa's head as a trophy, when he cut it off, which he than sent to the gods, right? That means that Medusa got into Tartarus cause she died. My question now is: what would happen to Medusa's head if she had gotten through the doors of death? Would her head, which is with Percy, vanish? Or would Medusa not be able to walk through the doors of death and is now laying headless in Tartarus? Or are there gonna be two heads of Medusa if someone beheads her again? And is it possible to petrify medusa with her own head from her former life?