Well, I'm pretty sure William is replaying his death over and over again. When he became Springtrap, at the end of FNAF 3, Michael burns down Fazbear Frights. Then Springtrap comes back as Scraptrap in Pizzeria Simulator, that place burns down, and then, Scraptrap comes back as Burntrap, and then... (SPOILER ALERT) ...One of the endings to Security Breach, apparently either Glamrock Freddy burned down the place and Afton was inside the Pizzaplex or Molten Freddy was with Burntrap and then Molten Freddy hung Burntrap for what he's done in the past and he died that way. But, if there are more FNAF games, William will possibly come back alive but we're not sure yet.