No real idea on the de-pressurisation/fire conundrum.
Off the top of the head I should have thought initial smoke dissipation followed by increased fire problems because of increased oxygen supply?
I think that there was a lot that never came out concerning the Helderberg. I don't think the aeroplane broke up before impact. I do seem to remember that the fire started in the rear hold and that the FO either couldn't get the interconnecting door fully open and/or that he was unable to access the fire extinguisher which was behind the door?
I have always rather felt with this incident, that it would be rather injudicious to enquire too deeply as to all the whys and wherefores.
