If they pulled the busses the plane indeed would go silent. It was probably a serious event and they simply were occupied with controlling the plane and trying to fight the fire. Aviate, Navigate and lastly communicate. There are two types of fires. Electrical might not be as fast and furious and there might or might not be incapacitating smoke. However there is the possibility given the timeline that perhaps there was an overheat on one of the front landing gear tires and it blew on takeoff and started slowly burning. Yes this happens with underinflated tires. Remember heavy plane, hot night, sea level, long run takeoff. There was a well known accident in Nigeria of a DC8 that had a landing gear fire on takeoff. A tire fire once going would produce horrific incapacitating smoke. Yes, pilots have access to oxygen masks but this is a no no with fire. Most have access to a smoke hood with a filter but this will only last for a few minutes depending on the smoke level. (I used to carry one of my own in a flight bag and I still carry one in my briefcase today when I fly).