I think the thing is T, is that the switch has NOT been just flipped. It's been gradually turned off for months if not years. It only seems like as instant thing. They started drifting into their own little world way before we knew about it.
Their spaceship set off, we were left on earth, every now and again they phoned home (acted normal) but were still out in space. Eventually they got too far away to send a signal back. That's when we suddenly thought...Where ARE they? How could they leave just like that?. They however, were already on planet self.
