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Any change to a non-refundable fared cruise causes forfeit of the deposit.
I cancelled a person traveling with me and lost not only my deposit but also all OBC even though I remained on the cruise. On a subsequent cruise, my traveling partner was just a "no show" and I saved all of my OBC.
If I use Future Cruise deposits with a $200 deposit, I book non-refundable fares. For cruises with higher deposits (Club Orange), I pay the higher refundable fare. Note that HIA fares and refundable fares permit changes without loss of deposits.