ummm,,, in my case it was my wife who couldn't go but I still went, I canceled her and I had a pay a $99 cancelation fee. which was basically a non refundable deposit, plus I lost $150 OBC which she had so... without knowing the details of your deal or contract, I would "as others advised" leave it alone,
both of my siblings spouses have missed cruises as well they just showed up and said there not gonna make it....OBS was added to their sail and sign for port fees and taxes.
now with all of that being said if the cabin was booked as them as the primary and booking the rate under there VIFP code "like a free cabin" then you might want to get better advice because that could turn into a different story.