Can the UCMJ reinstate some one after they are out of the military to face charges ?

The UCMJ, which is Non-judicial punishment, will not reinstate a service member to active status, however, JAG, through that service member's branch can and will call that person back to face a court martial. It depends on the crime, jurisdiction of said offense, and agreements that the military and the civilian authorities make. Examples: A retired E8 was recalled to active to be tried for murder at Fort Bragg, late last year. He had already been tried in a civilian court of law, however, with new DNA technology, more evidence had been gathered, and he faced a Court-Martial from the military side. In addition, the former SPC from 101st AIRBORNE, is/was being tried as a civilian in Federal court for the and murder of an Iraqi girl. The military chose to allow the Federal court system to try this case. My guess on that, would be because the Federal court system would impose stiffer punishment than the military court; however, life in prison is life in prison.