My theory is they ripped off the plane. The pilots are converts to the religion of peace, they went up to 45k shut off the O2 killing everybody, brought it down again and landed it - God knows where - and are planning to use it kamikaze style or God knows what. Bottom line: I highly doubt it was hijacked. The pilots were involved.
This means that at 45,000 feet, the passengers would likely feel the same cabin pressure as at normal cruise altitude. There is no reason to believe that supplemental oxygen would have been required. Or that passengers would not have been able to survive, if in fact the aircraft did climb to 45,000 feet.
http://www.forbes.com/sites/johngoglia/2014/03/15/malaysia-air-flight-370-could-passengers-have-survived-777-ascent-to-45000-feet/
Your theory may be correct.