Though the crazy amount of universe and timeline disagreements in Marvel's universes can fuck up any hard facts this is what I figure. He was in the field when he fell out of that plane into the ice so he is not discharged he is considered MIA (you might find this http://en.wikipedia.org/wiki/Missing_In_Action helpful especially the World War section). Though it is possible that he was discharged when he was recovered I don't think he was. There are a lot more people separated then discharged (http://www.answers.com/topic/military-discharge#Reasons_for_discharge) The major point of a discharge is over benefits and if being discharged gave his survivors benefits well it's a moot point cause he didn't have a wife because he left his girl to become a Super Soldier and his parent's were dead before he joined up. So what would be the point in officially discharging him. In our time it doesn't look like he's discharged either to me. He is in the service of SHIELD which for all it's voluntary nature is under a branch of the military (http://en.wikipedia.org/wiki/List_of_S.H.I.E.L.D._members) I believe he is still an active member of the army until he retires finishes his enlist time or dies...(this depends on what universe you're following).