Dyson and John turn their keys at the same time and open the vault, revealing the magical chip and the robot arm. John breaks some stuff, and they leave with the goodies.
The SWAT Team enters the building with breathers and guns. Arnold observes that it's time to go, as Dyson looks sad at the prospect of blowing up his life's work. He picks up the detonator just as the SWAT Team bust in and riddle him with bullets. Arnold and John are just outside the lab (on the other side from the SWAT Team), but Sarah's still in there, hiding behind a desk. Dyson is on the ground, shot up but still holding the detonator. Sarah fires off a few rounds to get their attention, and runs out. She ends up in a room with no exits, but Arnold conveniently walks through the wall to get her. He blows through a big metal door, and the three of them leave.
Arnold, John, and Sarah get into an elevator. Dyson is left in the lab as the SWAT Team creep in. He's hyperventilating, because he's holding a heavy object immediately above the detonator. The SWAT team wisely scrambles, and Dyson dies. Kaboom. The parking lot is full of fire and smoke. And here comes Officer Robert in his mirrorshades.
The elevator reaches the first floor, and the SWAT Team sends in a gas grenade as Arnold steps out. Sarah and John share a breather while Arnold goes out to deal with the problem. This, by the way, is the time that he says, "Stay here. I'll be back." Is that the lamest catchphrase ever or what?
Arnold walks out of the smoke, ignoring the orders to lie on the floor, face down. The various officers riddle him with bullets, exposing metal, but he keeps walking. He takes out a pistol and shoots each officer in a leg until he gets to the grenade-thrower, which he uses to dispose of the last two in the lobby, as well as secure the parking lot. Then he walks around, taking people's gas masks until he gets to the SWAT van. This time, instead of hotwiring it, he finds the spare keys hidden above the sun visor. Then he drives the van into the spacious atrium, all the way back to the elevator. Sarah and John get in, and it is time to leave.
Officer Robert has driven up to the third floor on his police motorcycle when he sees the van race off. The helicopter is hovering at just the right height for him to drive through the window and jump onto the copter. He breaks the windshield with his head and oozes in all liquid-metally. Once he's in the co-pilot seat, he tells the pilot to "get out." The pilot, knowing what happens to no-name extras who don't know their place, promptly jumps out. And Officer Robert is off after the van.