This is not how it was supposed to be, back in the days of "mission accomplished."
They came as all-conquering imperial overlords, sweeping away an enemy dictator and trashing all before them. They will leave after painstakingly negotiating how they get out, buying as much acquiescence as they can, leaving a destroyed country, more than a million more people dead than if they hadn't come, and some five million people displaced from their homes.
At least in part, they will leave because they can't afford, forever, to ignore the international law they tried to sweep aside with their pre-emptive invasion (usually called "aggressive war" by those on the other side of the guns.)
They will leave because they can't afford to stamp out the natives' resistance. They will leave because the Lilliputians have out waited them and tied them down.
And there is no sign they'll even get the oil.
They probably won't keep their word according the "timetable," but everyone knows that. They will weasel and "reinterpret." But they will leave Iraq.