Beware of cruise lines that offer you some sort of protection plan. Many of these tend to be fairly limited and are often based on a voucher system. I know I like to shop around for the best deal. I also like to get the best policy for my money. Third party travel insurance is often much less expensive than cruise line insurance and includes way more benefits.
Bottomline, I’d rather get my money back and not get some sort of voucher for future travel. Also if the cruise line or travel agency goes bankrupt, the plan that you purchased from them won’t cover you. Travel insurance from a third party is the only way to protect your trip investment should the cruise line go out of business.