Whether to depressurize to 25000' and continue or to ditch: in either case you're flipping a coin and taking your chances.
In both cases you'll be in no-mans-land, but the distinct difference with the ditching is that IMHO you'll be better able to judge your chances (day vs night, choppy ocean vs calm waters etc) instead of hoping and praying that the fire doesn't damage any vital components while you're counting down the minutes (or hours!) to the nearest diversion airport.
Those are going to be veeeeeery long minutes (or again, hours) sitting on top of an uncontrollable fire in the middle of the Pacific, Atlantic or the more uninhabitable parts of this planet.
