If you are referring to the Passenger Vessel Services Act (PVSA), cruise lines are supposedly pretty experienced at dealing with collecting the fine (~$800 USD) for passengers who miss the required foreign port of call. If you missed embarkation on a flight that they booked, I would think that either the cruise line or the travel insurance would pay the airfare and PVSA fine to get you to the first port of call for boarding.
Although the laws for crew and employees may vary from paying passengers, I was on a Norwegian Dawn cruise where they offloaded a comedian and picked up a new one during our Cayman Islands port call. I was on the tender with the departing comedian carrying his suitcases, and joked that I thought that his show the previous evening was good enough where they didn't need to throw him off of the ship. He said that he was flying directly home to the USA, since he had been on the cruise circuit for almost a year and wanted to see his kids.
The funny part was that I was sitting in the reserved balcony seats for the new comedian's first show. As the warmup act was on stage, he plopped into the seat next to me and was asking in the third-person about what I knew about the main act (him). Recognizing him from the poster at the door and playing along, I told him the story about how the captain put the last comedian off the ship at Grand Cayman, and how that comedian didn't want to talk about what happened on the tender ride to shore (none of it true). He then admitted who he was, that he had just flown in from the USA, and was in a panic because he had never performed on the cruise ship circuit before and was afraid that the last comedian was involuntarily disembarked because his act was too dirty for the passengers! Did I mention that I love messing with comedian's minds?
Let's just say that his first show was, um, funny to me for the way he was fumbling for "safe" material.....