This is totally implausible.
The hijacker's mission was to fly the plane into some building. They couldn't have cared less what the passangers were doing as long as they, the hijackers, had control of the plane. They would have continued on their mission.
The passengers forced that plane down, one way or another.
I respectfully disagree. I think it's much more plausible that the terrorists, being inherent cowards, were in turn completely terrified that they were losing control of the situation. They would rather face a disgusted allah in their afterlife and explain to it why they failed rather than have to deal with a mob of vengeful passengers. Remember allah’s finest had just slashed the throat of a stewardess or two. Once the passengers turned against them and knew they had NOTHING TO LOSE, the terrorists would have even eaten pork out of a jew’s bottom rather then face their wrath.