I am really struck by the absence of signs of life in the cockpit after 1:36
Are we inferring a Helios 737 replay here? If the flight crew was insensible then it's likely that all on board were. If the aircraft then flew on into a CB, suffered an upset and nobody was conscious to manually intervene, it could be just a variation on that theme. Time of useful consciousness at a cabin of FL350 is a mere few seconds. However ACARS recorded no loss of pressurization, so what other form of subtle incapacitation is there, other than poison? Both crew fell asleep perhaps and woke with a start at autopilot disconnect - after entering a large cu-bubbly?
.
Not sure whether or not there's any
other evidence to deny flightcrew disinvolvement as a theory (or for that matter, any viable scenario - short of an MS990 replay - in which it could play out). However it could also explain why no significant diversions around heavy weather along track were carried out.
.