[diogenes ghost]

".....dead from sudden decompression."

Not quite. Sudden decompression is quite unlikely, it simply never pressurized to start with.

[Red Badger]

Possibly, but what accounts for the transponder and other comm equipment being turned off?......

[beelzepug]

Shirley there must be an indicator that shows if the plane is pressurizing as it is supposed to. Once you go past 10K feet, the onset of hypoxia becomes more and more of a threat. Well before the plane had reached cruise altitude oxygen masks should have deployed.