The deaths in the Moscow theatre were not caused so much by the gas, but by the lack of immediate basic first aid being administered on the victims. This was apparent from a recent BBC (I think) documentary on it. The plan was perfect, the execution was perfect, but nobody thought about basic first aid.... Casualties (still alive) were dragged out, and laid face up in the street where they died. Simply putting them in the recovery position would have saved many many lives for example, so that when the vomit due to the effects of the gas, they dont choke on the vomit - that was the biggest tragedy of the whole thing!
However, were you to do the same thing in the air, you would have similar problems. Who is going to administer first aid if only 3 of you are concious, and 2 of you are flying the aircraft?