I thought in an emergency descent the a/c always maintained positive G by rolling/pulling over.
To start a rapid (emergency) descent there is no need to roll/pull over. In fact that is a good way to find yourself in an inadvertent unusual attitude which could be fatal if at night or in IMC at that high altitude. Today's airline pilots may be experts on watching or monitoring the automatics fly their aircraft, but probably not crash
(joke, Joyce) hot at manually flying at high altitude. If they start rolling and pulling while flying manually at high altitude, you can just about guarantee a handling problem which leads to a more serious flight safety event
A
gentle push-over straight ahead is all that is needed to start the rapid descent. There may be local ATC rules that require the aircraft to be turned off the air route before starting the emergency descent but not everywhere around the world.