The length of the war depends on how nasty Iraqi citizens become. If they start fighting like the Palestinians do with the Israelis then I expect the US to fight back similar to Israel - with might directed at civilians.
As to how long forces will be there - as I have written before - I am betting that there will be US occupying forces in Iraq 20 years from now.
As to how long forces will be there - as I have written before - I am betting that there will be US occupying forces in Iraq 20 years from now.