I don’t think they’ll go to GCM. I think it will be administrative.
Because I don't foresee him accepting any kind of plea, I think the chances of him avoiding court-martial and being administratively separated instead, are almost non-existent.
You can't have officers (especially an 0-6), publicly defying command and the CIC, and not prosecute fully, especially when there is a history of prosecuting junior officers and enlisted for the exact same offense.