Per DoD 4515.13-R, "C6.1.9. Conditions of Travel, there is no guaranteed space for any traveler. The Department of Defense is not obligated to continue an individual's travel or return him or her to point of origin, or any other point. Travelers shall have sufficient personal funds to pay for commercial transportation to return to their residence if space-available transportation is not available."
If you plan to travel Space-A, contact the Air Mobility Command (AMC) passenger terminal(s) where you plan to depart from. The terminal staff will have the most-current information available.