Then it comes back on again, because he's got "alternate power." He pulls the spike through his body and gets the gun.
John is exhausted when he hears Sarah yelling for help. He gets up and goes to find her. There she is, and she looks awful. But right behind her is the real Sarah! You know how they made it look like there were two Linda Hamiltons there? They used Linda Hamilton's actual identical twin sister. Again, not really a "special effect" so much as "careful casting." The real Sarah has a shotgun. John gets out of the way and she starts firing. Did I mention that they're on a high platform above an enormous vat of molten metal? Sarah takes several shots, each one pushing Officer Robert (because he quit looking like Sarah once the real one showed up) closer to the edge. Finally, he's about to fall; she cocks the gun for one final blast...and she's out of ammunition. Officer Robert heals up the holes in his torso and looks at her. He waggles his finger in a "no you don't" gesture. Arnold appears on some big conveyer-belt thing. He shoots at Officer Robert with his Big Explody Gun, which causes Officer Robert's torso to pop open before he topples over into the molten metal. He thrashes around, screeching and turning into the various people he's imitated before he finally just melts. What a world, what a world.
John goes to help the horribly wounded Arnold. "I need a vacation" says Arnold, which really makes no sense. The three survivors look down into the vat of metal; John tosses in the arm and chip from Cyberdyne. Arnold points out that there's one more chip (in his head!), and that it must be destroyed, too. Sarah has to lower him into the vat. John throws a perfectly understandable fit as the perfect father figure slash/coolest toy ever prepares to destroy itself.
What? What did Arnold just say? "I know now why you cry." God. Sarah, hurry up. I'll lower him in myself if he doesn't stop talking like that. Aww. One final hug from John. And a handshake from Sarah. I'll forgive him. This once. But if he says anything else stupid on his way into the metal, forget it. As Arnold goes under, he gives John a thumbs-up, and the computer-vision shuts down. John takes it hard.
More voice-over from Sarah, about the value of human life. Close credits. Play that Guns 'n' Roses song again. Wonder where to submit a chit for two and a half hours of wasted life.