WRT to crew incapacitation; the aircraft was shown steady at 35000 feet so presumably the auto pilot had been engaged not long after departure. Crew incapacitation at this point would mean the aircraft simply flew on at 35,000 till fuel exhaustion.
This
Aviation Herald report has the crew in contact with ATC as well so incapacitation at that point can be ruled out. The report states that both radar and radio contact was lost around 0122 local.
It will be interesting to see primary and secondary radar traces from that point on. The lack of transponder information from then on points to either massive electrical failure, or deliberate switching off.