AWOL (absent without leave) — в самовольной отлучке, в самоволке
Used especially in the armed forces when somebody has left their group without permission

be/go AWOL

Example 1: He's gone AWOL from his base.

Example 2: Two soldiers had gone AWOL the night before.

Example 3: I guess the officer couldn't handle the war, because right when things got rough he went AWOL on us. (Samantha)

an AWOL employee
be/go AWOL {of an employee} — прогулять работу, не явиться на работу (не сообщив об этом предварительно)

An employee is typically considered AWOL if he or she fails to call-in and report the absence prior to the start of the scheduled shift.
If an employee is AWOL from work for a predetermined number of consecutive days, that employee is considered to have abandoned his or her job and is terminated.

Note: This term is usually used in the context of a military situation, but is also used by civilians in other contexts (as a term to describe anyone who has taken off or is missing/ to deem anyone who leaves a situation without notifying anyone). Often used jokingly.

Example 1: My mobile phone's gone AWOL again.(= lost or missing)
Example 2: The cat's gone AWOL while we were on holiday.
Example 3: The guitarist went AWOL in the middle of the recording.

A term that USED to be used in the military to mean not being at your post or duty station at the required time. Civilians still use the term but the military uses the term UA (Unauthorized Absence) now.

...Civilians still say AWOL but we use UA in the military. (urbandictionary)