 What would've happened if Alan had not made it to the switch?
Frowning, worrying about the sounds, Alan momentarily forgot to watch his step until his foot suddenly plunged into an ant hill, throwing him to the jungle floor. Without pausing to think, Alan leaped back, and fell sprawling over a bush just as one of the robots rolled silently up from the right, lowering its blaster barrel to aim directly at his head. The metal killers, tuned to blast any living flesh, would murder them the instant they stepped from the ship! Apparently the robot hadn't sensed him yet, but Alan didn't know what the effective range of its pickup devices was. Alan, lying in the mud of the stream bed, felt the earth shake as the heavy little robot rolled slowly and inexorably towards him.
 The next group of people would have been caught by surprise and killed.
 The robots would have gone on living unnoticed by people, doing as they wished with the planet.  The next group of people would have been caught by surprise and killed.  Pete would have been the last hope of the people on the planet's surface.  Peggy would have had to build new radio transmitters after the old ones were destroyed.