I think the worst case scenariois the Swiss Air with the fire being in an area where it wasn’t possible to get fire supressant to. The whole idea of ETOPs is that the aircraft is able to carry out a diversion from the ETOPSs rule distance in the case of many problems including a fire in the hold. The B767 has 2 fire bottles for the holds. On a fire indication the first bottle is discharged. 80 minutes later (or on final approach, whichever is later) the second bottle is discharged. Both bottles have a measured discharge rate to ensure the fire protection for the full ETOPs 180mins. The extinguishant is highly toxic and therefore any livestock in the hold would not survive.

As WD mentioned, most cases are not reported in the media unless it is a smoking hole. I can assure you these things do occur but unless you are reading the incident reporting books of all the authorities around the world, you won’t see them.

If we do get an uncontrolled fire we can get the aircraft on the ground from cruise levels in 12 minutes. I have had a sim detail where we did exactly this and it works.