The ship would need to be designed around it, but the battery could be set up in a way to allow it to burn out without affecting the rest of the ship at all, it is not that hard to isolate a battery from the rest of the system.

Although it would be better if the battery is at the bottom of the ship so there would also need to be some sort of air exhaust system for when that happens, hopefully one that prevents the fumes from reaching the passengers at all but I don't think that would be possible without a chimney.

Almost as bad as a fuel oil fire on a cruise ship.

There's hope that sodium-ion tech will come to the rescue, here. The energy-density is bordering on 'good enough' but it's not quite there, yet.

There's other technologies that they're trialing for boats that seem silly but works on paper at least. We're currently building a ferry with a massive flywheel to store lots of rotational inertia to convert to electricity, which on the face of it is bonkers but again, the maths says it's good.

Is LFP an option ? Thermal runaway, O2 venting, they go away AFAICT.