Not let them on would be my guess.
Another deep analysis by DoodleDawg
What do you think they'll do with them?
According to recent stories, people who have COVID and not been vaccinated who take a Royal Caribbean cruise would be banned from the casino and most specialty restaurants. They will have to wear a mask when not on deck, will be restricted to one floor in the main diningroom, one section of the theater for shows, and may or may not be allowed off the ship in ports - that is up to the country in question. The reason I know this is that the cruise line has said that is how they are handling non-vaccinated passengers. Have a nice trip.