I have canceled excursions while on board (my mom had stomach issues) and been refunded to my Sign and Sail account. Cheers I think you need to cancel before you embark. Pretty much everything (restaurants, spa, etc) that you pay for ahead of time should be refunded to you if you don't make your cruise in the way that you initially paid for it. Since I use Carnival gift cards for almost all my Carnival purchases, I would be refunded in gift cards. That would be bad if I never wanted to sail with Carnival again, but since I have 5 cruises in my Cruise Manager I will just apply the gift cards to those future cruises.
I hope you and your DH get to go on your cruise!!