Tricky one, 'cause if you evacuate, then people will get hurt going down the slides, however, if you don't evac, and then fire suddenly erupts whilst pax go down the stairs, then even more casualties will occur.
I guess if you've still got your 'cargo fire' indication on the flight deck, and the fire service can't make a proper evaluation with the door shut, then I guess you have to think the worst, and get the pax out down the chutes.
Happened to a BA Classic which landed in the Azores with a cargo fire warning, and the Capt evacuated the pax down the slides in very strong winds (one slide went up over the fuselage if I remember correctly!).Turned out the fire indication was nothing more than fruit in the hold sweating and giving off vapours.
Just got to do your best on the day.