Back to our regularly scheduled programming...

So if our hypothetical bad guy used altitude excursions to disable everyone in the back, why did the airplane fly on for hours and then vanish? What was the point of it all then? Maybe just an unbalanced individual like what was alleged in the case of Capt Button? But if there was a rational motive (terror, theft of cargo) then why didn't it happen?

A flight 91 scenario is possible but it seems it would have happened much sooner, if at all.

How about this...someone in the cockpit could survive in the high flight levels ONLY if he used the appropriate setting on the oxygen mask, and used it properly. But any little mistake in that and the perpetrator would find himself disabled before he knew what hit him. Also...if he flew above the 30's the mask would NOT protect him from the bends unless he had pre-breathed pure O2 long enough to purge all the N2 from his body. He wouldn't have had time to to do that, even if he knew he needed to. Perhaps the perpetrator inadvertently took himself out along with the pax during that altitude excursion, and then the plane flew on AP following whatever route the perp had programmed until it ran out of gas.