<sarcasm>Sure - cut off oxygen from the fire - that's the best approach. </sarcasm>
Any displacement of toxic/poisonous fumes from the lungs of people is probably a good thing. The oxygen flow from the generators is so low compared to the volume of air in the cabin that not dying of lung damage is worth that change.
The fire is out in the engine coming in the normal ventilation supply and unaffected by cabin oxygen levels and that supply should have been shut off ASAP.