Any additional obc from a TA is refundable, so the $308 is. Leave it un the account and it will be refunded to your credit card on file with the cruise ship, you do not lose it. I just did this on Ascent 2 weeks ago, I saw a refund on my credit card 2 days later. I am cruising in 4 weeks and getting $195 non refundable and $508 refundable. The ta also gave me the option to issue a check after the cruise, I just tell them to add the total for on board. The $195 will be used first, if any left over comes back to me.