I'm under the impression that computer controlled brakes, like power steering, default to mechanical control. So if the engine starts revving without his consent the driver should still be able to apply the brakes enough to disable or slow down the car.
I don't think that's always entirely true- look at the deaths that occurred with the Toyotas where the accelerator became stuck depressed, obviously shifting into neutral would have been a better choice, but they were clearly unable to provide adequate breaking to stop.
