This information is correct, but there are some other aspects that you must be aware of. First, you go to the Purser's desk to request that you need to take advantage of the guarantee. There will be paperwork to fill out. Secondly, you must pay for your own transportation from the dock to the airport AND you must pay for your airline ticket home. Carnival will reimburse you the cost of the ticket only. Should there be a scheduling issue where you must spend the night before flying home...that expense is out of your pocket for hotel and meals.
Once you are home, submit the paperwork and receipts for the airfare and it will be refunded to you.
Fortunately, we have never had to use the guarantee. And (as with anything) always know exactly what is involved before making the decision to "jump ship".
Hopefully you will never have to find out first hand!!