Unclear from your post if you know this or not but large aircraft (almost all turbine powered) have fire extinguishers for each engine and other areas. Most planes that catch fire just shut the engine down, use the extinguisher then land it is not that big a disaster if dealt with promptly and correctly. I am sure many many aircraft have had fires mid Atlantic/Pacific and landed fine even though they are multiple hours from an airfield. If the fire is severe enough to burn regardles of the extinguisher and airspeed then yes you will probably have a much bigger problem that will result in a crash if you cannot land very soon.