I had used to have a copy of the Margo report on the Springbok 295 accident, the CVR indicates that the crew may have attempted to aleviate the smoke problem by opening one or more of the ac doors.
Also the fire that eventually brought the aircraft down was actually a re-ignition of a fire much earlier in the flight, this is where it gets complicated....none of this is mentioned in the report.
Not sure if the plane broke up before impact.
I have a question with regards to a cabin fire, as a last resort, what would happen if you depressurised the cabin?