We have no ideas beyond some possibly educated guess-work as to what happened here but I do have a question that can be answered by someone with the relevant experience. As a 10,000 + hr career pilot I'm not exactly a newby but have not any experience with the latest sophisticated systems being introduced on modern aircraft.
Q. Is there something preventing pilots of these aircraft from simply hitting a 'disconnect' button, listening for the 'C' tone and then getting on with flying manually ? Not suggesting that this is relevant to this accident.