Own jetpack won't work at extreme height, too cold and no oxigen, but the whole plane might be possible to first eject slowdown parachute at tail then lots of parachute/airbag around the body, thus ATC can override with an emergency brake and shutdown the engine
I think you're underestimating how much parachute you'd need to slow down a jetliner traveling at 600 mph. And a parachute to slow down an entire plane, assuming this was physically and mechanically feasible, would ostensibly be deployed from the cockpit, which makes this a solution that wouldn't have worked in this case, since the co-pilot locked out everyone who didn't want to crash the plane.