That is a question better answered by an admiralty lawyer than a professional mariner (90% of which are sea lawyers, but that is a whole different animal).
A flag state will determine which requirements the Vessel will have to meet with regard to trading certificates. Most of the flag states are signees to various international conventions (MARPOL for pollution, SOLAS for safety, Load Line for stability, etc.). Of course, these regulations also differ depending on the type and size of the Vessel and the intended or actual service.
Meeting the various conventions and flag standards are often a requirement of any insurance policy/implied or actual seaworthiness. I think THAT is where this case will have the most interest. I would assume that one of the sides would have some kind of insurance, either H&M or P&I. That would also determine which country/locality would have the juristidiction of any disputes. Of course, as I said, an admiralty lawyer could answer this better. Especially in the absence of any insurance. Then you deal with liabilties. Accusations of piracy aside.