There is no right or wrong answer and it is an ever evolving situation. I did the same emergency many times on recurrent checks and the basic do's and don't were always hammered home and that stayed with me. I did experience a similar situation and eventually we moved away from evacuating down the slides and even steps on the runway.
Only indication now as to whether you actually have a fire in the hold is the temperature in the hold and you can bet that all eyes were on that gauge and cabin crew were feeling the floor temp of the aft cabin.
We got an "Aft Cargo Fire" warning in a 744 600NM west of the Irish coast whilst heading home from Miami in 2004. I was looking at the overhead panel at the time and the First officer was checking the window heat on the side panel so it came as quite a shock. We completed the checklist items (basically reduce airflow and fire the first bottle), declare an emergency, leave the NAT Track system and headed for the nearest suitable airport, Shannon in this case, at max warp factor and then woke up the relief pilot who was on scheduled rest.
"Aft Cargo Fire" did not go away and we did not expect it to as we had blasted the first bottle and it would have been quite a fog in there which would keep the warning on as the fire detection system merely detects reduced visibility.
After 15 mins, Aft Cargo temp remained absolutely constant (low) and as there was no sign of heat on the aft cabin floor it persuaded the three of us that perhaps there was less of a chance of a fire in there.
We ran the DODAR* again and the last is R is Review, our first DODAR had us going flat out to Shannon and an emergency evacuation down the slides with the prospect of a ditching if things detiorated, the subsequent reviews over the next 60 mins gently downgraded the situation to steps at the end of the runway in Shannon and the ultimate one was disembarkation down steps close to the terminal after a Fire crew inspection.
We landed in Shannon having fired the second bottle on approach. On landing there were steps at the far end of the runway and fire crews all down the runway and we came to rest by the steps. Even evacuating down steps in the dark at 5.00 in the morning out on the runway has its problems as people go walkabout so after a chat and cursory inspection with the Fire Crew (touching skin of rear hold to gauge temp and looking for smoke) they accompanied us on out final plan, passenger disembarkation down the steps in an orderly fashion 20M out from the normal jetty and then up the steps to the terminal building. This was followed by opening the hold surrounded by all the fire appliances available within 30 miles of Limerick.
It was a false alarm, there was no fire and we knew 30 mins into the emergency that the cargo manifest showed some pallets of fruit so we always had our suspicions. All the cargo was removed, the bags were removed, the First Officer did the refuelling and we got the pax back on board and flew home to Heathrow with empty holds. We got in our cars and went home having filed just an Air Safety Report, the company sent an aircraft to collect the bags and cargo from Shannon. Never heard a word from the company or anyone else ever again.
* DODAR. Works for just about any situation, aviation related or not.
D: Diagnosis O: Options D: Decisions A:Actions R: Review