Just like other places in the past, they have walked in thinking they can solve what they perceive as the problem, only to find that they didn't even start to understand what the problems are.

In my post-war lifetime I can't think of any single place where they made the slightest bit of difference apart from a temporary reduction in the population and a stiffer resolve among their opponents.

So to answer your question, I think they will pull out as soon as it is politically expedient for them to do so - without regard for what they are leaving behind.

And if your conversation had been about Afghanistan instead of Iraq? .....