Here’s a short lesson from the official U.S. Army course on the subject, INFANTRY PLATOON DEFENSE, with tactics for withdrawal, delay and disengagement towards the end of the chapter.
“In most cases four to six snipers were ordered to rear guard and eliminate any enemy appearing; very good results. Use machine guns for rear guard only in emergencies since snipers delayed enemy's advance by one or two hits without easily revealing his own position.”
DISPERSAL & PRE-PLANNED ESCAPE ROUTES
Viet Cong, Vietnam: “VC will seek concealment in the local area in preference to panic and purposeless flight. The individual’s knowledge of fieldcraft, evasion techniques, and familiarity with the local area are decisive factors. If pursued to a settlement, he is taught to hide his weapon and other equipment and demand concealment from the villagers whose fear of possible reprisal from the VC may provide him temporary protection. His personal safety is the VC’S only responsibility. If VC personnel have to hide out for weeks before returning to their unit, this is acceptable as they have no requirement to be back by reveille, and in their absence, they leave no vital installations unguarded or in danger of attack.”