That's not "winning a war." If things go to hell in a handbasket after we leave, "going back and doing it again" is a confession that we lost last time. And after a certain point, one has to wonder if it's worth "going back in and doing it again" again.
It depends on the goal. Holding Iraq is fine, punishing Iran and Syria is priceless. We don't have to occupy them, just remove their leadership and do a lot of damage.