There's a lot of good sensible discussion here on this very serious topic. Much has been discussed with respect to the difference between a cabin fire, which would primarily cause death through asphyxiation, and the structural fire, which would obviously cause death as a consequence of structural failure.
Irrespective of which type of uncontrollable fire that you face, history shows us that you have about 5 minutes to get the aircraft on the ground (or water), 10 minutes at the most.
One poster asked of the experiences of wartime crew, as a young F/O I flew with a great many ex Bomber Command Captains, and their universal consesnus was that with an uncontrollable fire, you have 5 minutes to get out. They could get out, we have to get down and get on.
As a young 'Sixties' F/O in Australia, our Ops Manuals all advised that in the event of uncontrollable fire, "Land at the nearest suitable airport". After the Ansett Winton disaster it was changed to "Land Immediately". As the years advanced, and people forgot the lessons of history, the words subtly changed back to a compromise, "Land as soon as possible". My own philosophy never changed, in the event of an UNCONTROLLABLE fire, I will land immediately.
To my mind, the only possibly survivable uncontrollable fire is for the pylon mounted engine, but, in the past, even those have burned back through the pylons into the wing structure. Does anyone have any manufacturer's information regarding the survivability of uncontrolled engine fires with pylon mounted engines on more modern aircraft such as the B747 and A340?
Regards,
Old Smokey