> No, but modern jets need computer-aided control of flight control surfaces to keep the aircraft stable.
Most aircraft outside of fighter jets are aerodynamically stable. Loss of powered flight would mean the airplane will glide (in nominal operation). Even the 737MAX7/9 aircraft are still stable (although that brings up defining exactly what we mean by aerodynamically stable... )
Sure, but there is significant overlap between being stable and throwing around passengers, unfortunately.
Dropping 500 feet is perfectly okay for the aircraft and it will largely continue to not simply fall out of the sky past that.
In the case of military aircraft, they quite literally can't glide or maintain stable flight without the flight computer actively managing the control surfaces.
A 787 is perfectly capable of flying in steady state should the computer glitch.