Would routing exhaust into the main cabin be practical for starving a fire in a freighter, such as the UPS 747 out of Dubai?
I would suggest not.
I cannot give specific figures but in the case of Concorde, there was sufficient oxygen in the exhaust gas to enable the reheat to be used.
The Concorde fuel tanks were pressurised at altitude. I am wondering if the Concorde had still been flying today whether the FAA would have wanted/insisted it to have an NGS fitted.