The courts determine whether a cruise line is legally responsible to a passenger by reviewing the terms of the passenger ticket. I saw one judge literally pull out a magnifying glass to read the fine print buried in the ticket. The passenger invariably loses when this occurs, which is not surprising. The cruise lines have spent considerable effort drafting language which protects them from virtually every imaginable situation. The exception is when a passenger has been injured or assaulted - there is a federal statute which prohibits cruise lines from limiting their liability in these circumstances.
Cruise lines reserve the right to change their itineraries at their discretion.
Again, most tickets limit the cruise line's liability for theft. This seems reasonable enough. One reported case involved a passenger who reported the loss of several hundred thousands of dollars in jewelry. My only advice is to leave your priceless jewelry at home, or buy insurance before you sail. Passengers who are injured have to send a letter to the cruise lines within a short period, usually six months, advising the cruise line that they intend to seek compensation.