If the Iraqis don't want the Americans to help out, and Iraqis are pro-American (by local standards), U.S. troops, and commanders, are suggesting that they all depart as soon as possible. The Kurds are still very pro-American, and nearly all Iraqis are very hostile to Islamic terrorism. Mission accomplished.
This was always the plan. It is, in fact, the standard approach to these situations. Once the enemy is defeated, and a new (friendly, or at least less hostile and warlike) government is able to defend itself, you go home.
We could be down to 50,000 troops in Iraq in only 15 months, as Strategypage writes. I hope this includes a full "division" of four brigades in the Basra region to deter Iran and cover Kuwait, too. Plus another brigade in Anbar--say a Stryker brigade--for patrolling and reassuring the Sunni Arabs. Air power in the center and in the Kurdish region would be appropriate, as well.
Think of these as staying for 5 years and then we start drawing down a brigade per year as Iraqi forces mature until we keep just one in the south as a tripwire against Iran.
Air power, too could draw down to a token amount over time as the Iraqis gain conventional military air power.
Then we're mostly down to training missions and perhaps 10,000 troops total until we decide we don't need even those forces to keep Iraq upright.
That's my opinion, of course.
And all these timetables could be accelerated if we somehow get lucky and see regime change in Iran lead to a pro-Western government.
