Carnival's website says you can still go with a driver's license provided the trip starts and ends in the USA. If going to Martinique a passport is required if you are going ashore. There's some other comments in their recommendations as well in their "Know Before You Go" section. It's a good read.
After logging into Carnival's Website go to Manage My Booking > Booking and Order Details > View Balance Details > View Cancel Information. Clicking that will let you know if there are any penalties and there is an option to Cancel. I don't know what is past that point since I didn't want to cancel my own. Hope this helps.