Booked companion certificate for MSP-HNL with my husband as the companion. He is now unable to make the trip. Can I cancel his "companion" ticket without messing with my seat (used RUCs)?

I've read about splitting the PNR and then canceling. Is this a real thing that can be done? Will I be able to get the RUCs back from his ticket?

i'm not concerned about forfeiting the certificate and more about losing my seat as travel is in a week's time.

Thanks in advance!