The Companion is linked to the Member in the computer. While they may board and check in separately, WN has become very diligent enforcing CP infractions. When the boarding is done, and the linked reservations do not have linked passengers on board, expect them to look for the Companion and remove them. I would not want to be the one testing this system as the penalty can be harsh including cancellation of the RR account including, of course, revocation of the CP.

I have CP and fly as my own companion. In the early days when I was still trying to figure out the system and all of the steps to make it work, there were a couple of times when the computer did not register that both me and my companion had boarded. The OA came on, asked for me to raise my hand, and walked back to my seat to make sure that both of us were on the flight. I asked what happened and he said that the boarding scan showed that only the companion portion had boarded.