If he is deemed mentally fit and the evidence is there, then a trial.
Edited to add links
http://usmilitary.about.com/od/justicel ... /awol7.htmThe commander has many options to choose from. The commander could impose Article 15 (nonjudicial punishment), possibly imposing a fine, or restriction, or correctional custody, or reduction in rank, and then allow the member to return to duty. The commander could impose an administrative discharge, usually with either a general or other-than-honorable conditions (OTHC) discharge characterization. The commander could impose Article 15 punishment, and then follow it up immediately with administrative discharge proceedings (thereby discharging the person with no stripes on his/her shoulder and/or imposing a fine so they are discharged with little or no money in their pocket). Or, the commander could refer the case to trial by court-martial.
http://usmilitary.about.com/od/justicel ... /awol6.htmArticle 85 - Desertion. This is the most serious of the absentee offenses. Remember the primary difference between AWOL and desertion is intent to remain away from the military permanently.
(1) If a member deserted, but voluntarily returned to military control: Dishonorable discharge, forfeiture of all pay and allowances, reduction to the lowest enlisted grade, and confinement for 2 years.
(2) If the member deserted and the desertion was terminated by apprehension: Dishonorable discharge, forfeiture of all pay and allowances, reduction to the lowest enlisted grade, and confinement for 3 years.
(3) If the member deserted with the intent to avoid hazardous duty or to shirk important service (and example of this would be a member ordered to deploy to Iraq and then deserts to avoid the deployment): Dishonorable discharge, forfeiture of all pay and allowances, reduction to the lowest enlisted grade, and confinement for 5 years.
(4) If the member deserts during time of war: Death or such other punishment (such as life in prison) as a court-martial may direct.
Given that even the left keeps calling Afghanistan a "war" there should be no question that if the letter he allegedly left behind is true and the actions he took that night are factual then, Bergdhal did desert during a time of war and the punishment should reflect the crime with life in Fort Leavenworth being his reward for services rendered.
But, given that they even bothered to get him back only to have this PR disaster happen, there'll likely be no Court Martial so he can't be found guilty of desertion and he'll be quietly shuffled off to some obscure base to be released with no fanfare thus, preventing the current administration from getting anymore egg on their face.............and justice be damned.