I repeat, Unused onboard credit is posted to your credit card. I am speaking from experience. If anyone has had Unused credit and they did not get it in cash or as a credit to their card now is the time to post.
Go to the casino on the last couple of days and take out money on your ship account card to use up any OBC's. Just don't tell the staff that's why you're doing it. If you don't use the credits or take it out in cash you will loose them and the cruise line gains! We have always used all of ours by doing this.
And that is exactly why RCI is beginning to charge 3% on cash withdrawels on your SeaPass card in the Casino at the cashiers window AND the tables.