I like what nitpicker330 suggests.
Equally, from what others have suggested there is very little chance of sending Li batteries to their destination via the sea lanes, and no other. At least not yet. Commercial pressures abound. They are a greater force at work, but it seems an immediate solution could be to depower the batteries before shipment which removes their flammability. Added to that, shipment in a fire-proof container as an interim measure. I'd reckon Asiana will be doing something like that given they lost a bird. Others might take longer to come around, but it won't be long.
How long does it take to mandate this stuff once it's all figured out as necessary, desirable and, perhaps more importantly, cost effective? Waaaay above my pay grade, so back to mitigating the effects of a fire, should it break out, as interim measures.
On the subject of ditching: tough decision. Sully's case was not repeatable in this instance. At night, over land, on fire, no Hudson in sight...Sully's engines not working made flight an impossibility, unless they lit up again, to which Skiles worked tirelessly. Meanwhile, continued flight was a reality forced upon them. If we're questioning ditching, well, if it's a question that's only because the situation's not yet terminal.
Does being on fire mean you ditch? Only when you know you know further flight isn't an option. And there's the thing: you get a fire warning at altitude over water. You spend at least, AT LEAST, 10 seconds perceiving, analysing and acting in a co-ordinated manner. Now we're talking AT LEAST here, as any fiar dinkum pilot knows. To say otherwise is just not true. Do you spend eight to 15 hours of every flight on the edge of your seat waiting for the air molecules to just stop holding the airplane up?
No way, not unless you're Japanese. You don't sit there strategizing every minute of every flight, so a fire warning, any warning, will come as a surprise and you'll need time to analyse "wtf is this" before you act. That all takes time, so I reckon 10 seconds is a bare minimum for the circle to start with perception and end in action.
After that you divert immediately. But unless you're constantly strategizing and analysing your in-flight options, nearest airport, weather en-route, traffic to the left or right, who has the radio and why the **** Bloggs chose this moment in time to take a piss, then you're going to have to spend another minute, at least, be real, don't bull**** yourself, figuring out what dynamics have changed, where the traffic is, below, above, left or right; where is the nearest airport, no longer the nearest suitable; can we make it; should we put her down (land or sea), and then, "****, you mean we have to ditch?"
I have never ditched, but I've thought about it long and hard, as genuine posters here are doing. I would want to honor the Asiana guys by suggesting they were not panicking; that they were doing their level best to keep it all under control while they got their checklists done in a rapid but orderly fashion before deciding on what options were available. Sadly, it didn't work out. Nor will it work out in future if the same happens in another cargo airplane (no, Li batteries are not permitted in the lower cargo hold of passenger airplanes, or any hold of a pax plane for that matter, so don't worry 'bout that, poster).
Good luck if it's you.