I think the plan required a pilot in the cockpit and a hijack team in the cabin. One or both pilots.
If there was somebody else in the passenger list capable of flying a 777 and switching off the commo, that can be discovered fairly easily.
Any guesses as to what happened after the hijack itself went down? Any odds guesses that the plane is intact someplace? I think it was pretty clear from the beginning that it wasn’t mechanical failure. Stuff switched off and direction change would preclude a Payne Stewart type event.