And if I understand the Carnailval deal correctly: if the ship does leave they will get you to the first port at their expense.
This is a common belief but it is not based in fact. It's a cruise myth. Even if you book air through the cruiseline, if that ship leaves prior to your arrival at the pier there is no contractual obligation to get you on that ship. If you have insurance and followed the flight guidelines or booked air through the cruiseline you may well be re-imbursed for the flight to catch up to the ship. Also, the airline may provide you asssistance or comp you a flight to catch up but they may not. They nor the cruiseline is under no obligation to do so. Read your doccuments provided with your cruise and on your flight reservations. Your best bet for protecting yourself againt unexpected events is travel insurance. Otherwise the costs above will be at your expense in almost every case.
Annette, I'm shocked that cruiseline air was at competitive rates with what you could find with air booked on your own. If you change the flight to the day before they will charge you a $50. air deviation fee if you book your own hotel. If you add a pre-hotel through the cruiseline there will be no fee to change your flight to match your pre-hotel package.
Whatever you do, have a great vacation!