Tcas climb, the B767 has fire detection and protection in the cargo holds. But okay, say that the extinguishing system does not kill the fire, you're still in the same situation.
When you're dumping the pressure at crz alt, you'll have to drop the oxy masks and the real danger when using the oxy system is that if the fire catches that, you won't survive.
When the fire is also fed by flammable chemicals in the cargo hold, dumping the pressure would only make it harder for yourself.
During some flight safety fire training I followed a few weeks ago, we saw videos of cabin fires. On average, you'll have about 2-3 minutes from the time that the fire reaches the cabin till flashover occurs - at that time, everyone in the cabin will be dead.
Is it still allowed by law to have ETOPS flights in aircraft that don't have cargo fire protection?