For future reference for anyone else that may encounter this thread, I just went through this myself for a flight I have in two weeks and the companion has now decided to not make the trip. I called in, waited through the queue, and got an agent. Explained that I wanted to split the PNR, keep my flight (the revenue one) and cancel the companion. The agent immediately jumped in, made the necessary changes, automatically reinstated the Companion Cert (which I was willing to sacrifice, but didn't even get asked), refunded the fees from the companion ticket, and retained my reservation. I was quite happy with that, because rebooking that same ticket today would be about twice what it was when I booked two months ago. I did call in to the Gold Medallion number though I'm not sure if that really makes any difference for who you get on the phone, but having some level of status may have played an impact if anyone else ever has a different result. I don't think it did, especially since I'm still flying the (not cheap, since I didn't book even earlier when I should have) revenue ticket.