Speaking from family experience John Kennedy was not remotely interested in bugging out of Vietnam. He had 16,000 American personnel there and was increasing our involvement right up to the time of his death, even promoting the coup that killed President Diem in order to give Kennedy more control over Vietnam’s internal policy. The chaos resulting from Diem’s assassination was dumped on Lyndon Johnson, who managed to make a bad situation worse.
One if the more out-there conspiracy theories is that JFK was assassinated on the orders of Diem's widow.