Several years ago we had to cancel a cruise onthe Vista two days before departure due to my Wife suffering a very severe hemorrage in her right eye. We had purchased the trip insurance through Carnival.
Carnival did require a letter from her Opthamologist. After that we received a full refund for thr ctuisr costs, port fre, etc.
Carnival refunded our pre-paid excursions, gratuities and drink package fees almost immediately affter we camcelled. The cruise refund took app. 2 -3 weeks.