That's why I said it would be interesting to see how insurance companies decide on this. The insurance companies definitely would want this to be considered an act of war, I would expect, so they wouldn't have to pay out. But an act of war against a NATO country would be a much bigger deal, so I would expect that the governments of the necessary countries to not want this to be considered one and we'll have to wait and see what shakes out from all of this.

UNCLOS Article 113 seems to say (to this non-lawyer) that the merchant ship operating country is responsible for punishment, and the only protection is if the mariners can prove that they "acted merely with the legitimate object of saving their lives or their ships, after having taken all necessary precautions to avoid such break or injury." Article 114 says that the merchant ship owner is responsible for the cost of repairs.

So that means, if it can be proven that Yi Peng 3 was responsible for this, then it's going to be on the Ningbo Yipeng Shipping Company to pay, and the PRC to punish. From what I have been able to find, that is a small shipping company with just two ships, one of which is currently unable to operate due to being stuck in the Kattegat. I suspect that means that not much money would be available from that direction, and so I wonder if the insurance companies would be on the hook for whatever excess costs are born by the various companies.

I think you're conclusions are correct that it's most likely shipping company/insurance would have to pay. If there's no money I think usually they seize the ships and sell them.