lomapaseo
I would suspect that you are thinking jet FCOM here. I've never seen such a one on a t-prop.
Back to the question at hand, I would always treat a fire as real. Even at low speeds, any indication that would be visible would be about a km behind the aircraft unless you had a whopping big fire going. I would always pull the handle and head back S/E unless there was no way to stay aloft on one. My one experience was with a max weight HS748 on a hot day (28C) at 400' AGL. As turboprops go, that is about as bad as you are going to get. We shut down and returned on one. The only problem was that the captain selected gear down a bit too far out, and we burned A LOT of water/methanol to maintain until we made the runway! Turned out to be a bad fire wire, but who knew?
Given just about anything else with a turbine engine, flying on one with a professional crew (as opposed to a weekend flyer who logs about 60hrs a year)is much less dangerous than living with a POSSIBLE fire on board.
