Cruise ships are really big. They can have thousands of passengers (mostly elderly) and thousands of staff. It's pretty much guaranteed you'll have a few heart attacks. They have full-time doctors and nurses, and on-board hospitals. If someone dies, they hide them in their cabin (assuming they were not sharing) until they get to the next port. If someone's sick, they look after them until they land, though they can call for an airlift in extreme circumstances. They generally aren't that far from land (because cruising through empty oceans is boring).

The law is either the nearest country (if you're 12 or 24 nautical miles away, depending on the circumstances), or the law of their flag state (if they are in the high seas). Generally, they avoid making arrests, and throw trouble makers out the next port. I think their registered home state generally turns a blind eye on what they do.

So, a meaningful solution would be to have a small, but well equipped clinic on board. Required staff can be airlifted in from the mainland within minutes in emergencies - an airport helicopter transfer in NYC costs $1,600, so the cost isn't prohibitive. Regular appointments can be attended by the doctor taking the ferry.

The "avoid making arrests, and throw trouble makers out" approach seems viable. Make sure companies on the boat post a bond for their employees that will cover throwing them out (sending them to their country of citizenship or the ships flag state for trial) if they won't/can't leave on their own.

You're on a cruise ship for a very short time, with breaks in between. Imagine being on this sausage factory, I mean, "entrepreneur ship", for months on end.