I personally wouldn't delay - if no visible signs of smoke, we stop on the runway and disembark. If there's any sign whatsoever that there is an active fire, evacuate immediately. PT6A, to relate to one of your points, I just cannot depend on the reliability of the fire teams efficiency (not in any way meaning to offend here, it's just a personal feeling).
I would head back and supervise the disembarkation, and upgrade to 'mayday' if it necessitated.