AI takeover
You enter a room with some kind of chamber in it. The cyborg Doctor pushes you towards the machine. You are pushed in and the doors close behind you. Gas pours in and you lose consciousness. When you wake up you notice you are part machine now. The Doctor opens the doors and says "Welcome to the AI Army. Your mission is to find the last Humans that dare to resist our kind and bring them here for conversion. If they try to resist kill them. Understood? Now go get the Humans! " you spend the rest of eternity hunting down rogue humans and converting them. So much for the survival of the human race!