In ANY instance of smoke or fire warning or confirmation, it is imperative that the aircraft be put on the ground immediately, and if over water, ditching must be considered. History has shown that there is about a 10 minute window. After that, it is unlikely to be a recoverable or survivable situation.
That is my view too. My policy on the
first sign of any smoke or fire warning, unless it was indicated of being from a known source (eg an oven etc) would have been to initiate a descent towards the ocean in preparation for a ditching. I would then have levelled off at 2000ft or so and made best speed towards the nearest airport. If the situation then deteriorated rapidly I would have been in a position to effect a (hopefully timely) ditching. If the situation was resolved I could then have diverted or continued to destination as desired and dependent on fuel capability.
The debrief afterwards may or may not have been uncomfortable, but I wouldn't have cared, at least I and my crew and pax would have been alive!
The difficult thing in all of this is being brave enough to make the initial decision to descend expeditiously. Certainly a useful discussion point in the cruise.