If backup systems conk out
The plane is also equipped with battery systems, reserved for when all other systems fail. But since we're going down through worst-case scenarios, let's say those are also kaput. All is not lost! Though there is not a recorded instance of this in recent commercial aviation history, pilots train for this scenario in simulators all the time.
Commercial aircraft aren't designed to be gliders, but in an emergency they can be. In planes with hydraulics, pilots can control the rudder, stabilizer, and landing gear using only hydraulic systems. Even if one of these fails, most planes are equipped with multiple, redundant hydraulic systems (typically three) so that if one fails, the others can take over.
It's not so different in a plane with a fly-by-wire system. Those also have a mechanical backup that allows pilots to operate the plane if the power goes down
If all of those fail? You're officially on the unluckiest plane in history, and your landing is probably going to be a rough one. But it's also less likely than you hitting the Powerball. A commercial flight suffering total hydraulic failure caused by something other than an explosive has only happened three times since the 1970s.
The old-style 737 aircraft has a manual pulley system for rudder and aileron control, and can theoretically be controlled without hydraulic power. But you won't find many of those flying commercially in the United States.
So even if every power system on the plane fails -- a highly improbably occurrence -- your chances of survival are great. It might be terrifying, and might have you taking trains for the rest of your life, but it probably won't be fatal. The most likely case is you walk away with one hell of a story to tell.