His commanding officer gets to determine the punishment. He can select no punishment, non-judicial punishment, or can send him to a Court Marshall.
Article 86 of the Uniform code of Military Justice covers Absenses without Leave
http://usmilitary.about.com/od/punitivearticles/a/mcm86.htmArticle 86—Absence without leave
Text.
“Any member of the armed forces who, without authority—
(1) fails to go to his appointed place of duty at the time prescribed;
(2) goes from that place; or
(3) absents himself or remains absent from his unit, organization, or place of duty at which he is required to be at the time prescribed; shall be punished as a court-martial may direct.”
Elements.
(1) Failure to go to appointed place of duty.
(a) That a certain authority appointed a certain time and place of duty for the accused;
(b) That the accused knew of that time and place; and
(c) That the accused, without authority, failed to go to the appointed place of duty at the time prescribed.
(2) Going from appointed place of duty.
(a) That a certain authority appointed a certain time and place of duty for the accused;
(b) That the accused knew of that time and place; and
(c) That the accused, without authority, went from the appointed place of duty after having reported at such place.
(3) Absence from unit, organization, or place of duty.
(a) That the accused absented himself or her-self from his or her unit, organization, or place of duty at which he or she was required to be;
(b) That the absence was without authority from anyone competent to give him or her leave; and
(c) That the absence was for a certain period of time. Note: if the absence was terminated by apprehension, add the following element
(d) That the absence was terminated by apprehension.
(4) Abandoning watch or guard.
(a) That the accused was a member of a guard, watch, or duty;
(b) That the accused absented himself or her-self from his or her guard, watch, or duty section;
(c) That absence of the accused was without authority; and Note: If the absence was with intent to abandon the accused’s guard, watch, or duty section, add the following element
(d) That the accused intended to abandon his or her guard, watch, or duty section.
(5) Absence from unit, organization, or place of duty with intent to avoid maneuvers or field exercises.
(a) That the accused absented himself or herself from his or her unit, organization, or place of duty at which he or she was required to be;
(b) That the absence of the accused was with-out authority;
(c) That the absence was for a certain period of time;
(d) That the accused knew that the absence would occur during a part of a period of maneuvers or field exercises; and
(e) That the accused intended to avoid all or part of a period of maneuvers or field exercises.
Maximum punishment.
(1) Failing to go to, or going from, the appointed place of duty. Confinement for 1 month and forfeiture of two-thirds pay per month for 1 month.
(2) Absence from unit, organization, or other place of duty.
(a) For not more than 3 days. Confinement for 1 month and forfeiture of two-thirds pay per month for 1 month.
(b) For more than 3 days but not more than 30 days. Confinement for 6 months and forfeiture of two-thirds pay per month for 6months.
(c) For more than 30 days. Dishonorable discharge, forfeiture of all pay and allowances, and confinement for 1 year.
(d) For more than 30 days and terminated by apprehension. Dishonorable discharge, forfeiture of all pay and allowances, and confinement for 18 months.
(3) From guard or watch. Confinement f o r 3 months and forfeiture of two-thirds pay per month for 3 months.
(4) From guard or watch with intent to abandon. Bad-conduct discharge, forfeiture of all pay and allowances, and confinement for 6 months.
(5) With intent to avoid maneuvers or field exercises. Bad-conduct discharge, forfeiture of all pay and allowances, and confinement for 6 months.
Those are Maximums
Missing movement is like Desertion - you can be executed.