With the cabin pressurization turned off, there's not enough oxygen available at FL450 to remain conscious for very long and probably not enough to live for much longer, depending on one's age and physical condition.
The oxygen concentration is about 21% at sea level and only 6.8% at 29,000'. I don't know the percentage at altitudes greater than that or what is required to live.
Regarding Payne Stewart's Lear, they probably froze to death in their sleep if the oxygen deprivation didn't kill them first.
The Boeing 777 pilot in this interview says there is 20 minutes of oxygen for everyone. The bottom line is that it didn’t ‘t happen as some of these wild-eyed conspiracists are saying ... :-) ...
What altitude? Malaysian radar claims it went to 45000. That should not be accepted at face value because the kind of radar needed to accurately determine 45000 is not sitting on Malaysian soil. Yes, without O2, the passengers pass out after their emergency masks run out. The F/As have walk around bottles that could last for a long time. You don’t climb to FL450 to kill people, when FL350 can do it just as well.