Being a 777 driver, there is no doubting it is a wonderfully designed aeroplane, the redundancy etc. built into the aircraft is superb, if you HAVE to use it.
Even when you put a hose on a garden bonfire it still remains hot. Water has considerably greater cooling properties than the exstinguishing agents in the aircraft. So even with the cargo fire light out things are going to be mighty warm. If you don't have to I would have thought it was prudent not to test the aircraft structure for fire resistance.
brgds
CRS