As a passenger waiting for departure in a regional aircraft from Dulles to Philadelphia, I was quite annoyed when they insisted on returning to the gate and taking a later flight because the Captain's emergency air bottle was U/S.
Especially as the flight would have remained below 12,000.
And then I remember that flight - can somebody give the ref - that flew on and on and on over the Med until it ran out of fuel....the entire crew and a considerable number of passengers unconscious to the end.
Don't mess about with lack of O2....