Fortunately, most cargo fires occur during the early part of a flight, though maybe not soon enough (before I show up to the plane for my preference), so running back to the departure airport may be the choice (a lot of good it did UPS and Asiana admittedly). As for ditching, I spent a long time talking to a gentleman that had Boeing Clipper time (flying boxes after WWII). He said that they considered putting down on the open ocean largely unsurvivable, obviously with a lot of caveats. Certainly, I would attempt to verify I had a fire before using ocean water to put it out. On the other hand, the only way a ditching has a chance of being survivable is to land under control, so its a quick decision.
On another note, I am told that Li-ion fires are quite toxic, so egressing after ditching may be rather fraught as well.
In any case, management will have you off of payroll by touchdown, and the NTSB- or whoever- are sure it was pilot error.