20kN has it right. I will add if the plane is not depressurized, you won't be able to open the emergency doors. If it is depressurized, but still at high altitude, you will have to stay on oxygen to function, and so it would be hard to get to a door unless you are right next to it, and it would have to be an over-wing hatch door. I do think you could get out of a hatch with your rig on.
So you need two events:
1. A plane that is depressurized
2. A plane that cannot fly
If both of these are true, there has probably been a catastrophic air-frame failure, most likely a terrorist attack or a really bad engine failure that damaged the wing / tail and the fuselage, so in addition to having to deal with oxygen and getting to a hatch and opening it and getting out into a very high slipstream (300+mph?) the plane could be spinning or tumbling as well, a very challenging situation. You would want to stay on oxygen until below 20k ft, or try to hyperventilate on oxygen before exiting.