Do you have any idea of why the fire occurred?
In the history of helicopter aviation....how many simple engine fires have there ever been? By simple....I mean something like a fuel line leak that does not affect the Engine beyond causing a fire.
Commonsense would suggest the crew makes a decision based upon aircraft performance and any other factor that plays into the decision making process....and as soon as possible secure the Engine by means of the approved procedure.
That being said....are you sure the fire can be contained/extinguished by means of the approved procedure? What damage was caused by the fire? Has that damage harmed the aircraft to an extent continued flight is not a good idea?
Your question is way too limited.....beginning with the assumption you do in fact actually have a fire when you may only have a faulty sensing system.
I have had lots of Fire Lights illuminate....but have never had a Fire....and do not know anyone that has ever had a Fire. They are a bit uncommon unless something really ugly happens to the engine first.