It's every cruiser's worst nightmare: The ship sails without you. Most ships will usually wait a short amount of time for late-arriving passengers, but it's always at the captain's discretion. Since the ship will incur additional dock fees and need to burn more fuel to make up for lost time, most captains are loathe to stick around for too long. Here's what you should do:
If your flight is delayed or cancelled and you miss embarkation
Booking a flight that gets you to your departure city the day before you are set to sail is the best way to ensure that you are on the ground before the ship pulls away. If that's not an option, look into booking your airfare through the cruise line. If your flight is delayed, in some cases you'll be covered for any expenses you incur to reach the ship at the next port. For example, Carnival's Fly2Fun Air Program has an emergency hotline, and covers your extra airfare, hotel, and ground transportation expenses. In other cases, you can purchase insurance coverage through the line, such as Royal Caribbean's Travel Protection Program, which reimburses meals, accommodations, and catch-up transportation.
If you are late getting back from a shore excursion
The captain will always wait if a group on a shore excursion booked through the line is delayed, which is one way to be sure you won't miss the boat. You can still strike out on your own, of course. Be realistic about how much time you will need to get back to the ship (especially if the cruise port is far from the main attractions) and have clear directions in both English and the local language. Bring along the ship's daily bulletin, which will list the name and phone number for the port agent. Immediately contact that person if you fear you won't make it back on time. If the ship has already sailed, the port agent will help with the logistics of getting you aboard at the next port of call. You will be responsible for the additional expenses. It's smart to have your passport (or a copy of it) in case you do have to hop a flight to the next port, as well as a credit card for charging last-minute travel arrangements.