Here is the kicker . . . The oxgen bottle in the cockpit only lasts 30 minutes. Or thats what we plan on. Of course many factors determine the exact amount. Probably longer. But by regulations at least 30 minutes.
These are US FARs, but it's a safe bet ETOPS certified MH 777's could at least meet the following requirements.
(a) General. When operating a turbine engine powered airplane with a pressurized cabin, the certificate holder shall furnish oxygen and dispensing equipment to comply with paragraphs (b) through (e) of this section in the event of cabin pressurization failure.
(b) Crewmembers. When operating at flight altitudes above 10,000 feet, the certificate holder shall supply enough oxygen to comply with §121.329, but not less than a two-hour supply for each flight crewmember on flight deck duty. The required two hours supply is that quantity of oxygen necessary for a constant rate of descent from the airplane's maximum certificated operating altitude to 10,000 feet in ten minutes and followed by 110 minutes at 10,000 feet. The oxygen required in the event of cabin pressurization failure by §121.337 may be included in determining the supply required for flight crewmembers on flight deck duty.
So we have a crewmember who is a murderer, committing suicide, or a terrorist cell showing a government and other cell members how to do. Interesting either way.