bobbytables,
Your thought is reasonable. Without knowing the specifics about the pressurization problem there is a good chance the startle factor (from a non-working O2 mask) and TUC (time of useful conciousness) precluded that. If the decompression was slow there is a greater chance of that working. All training assumes the O2-system is working though, any other creative solution to the problem is a bonus.
Idle would be your best bet and if it got that far. You just have to assume you will wake up.