well less american soldiers will die and people in iraq will have to learn to sort out the mess themselves. this may seem hard initially, but it will work out. for example, the british left the subcontinent in 1947 and the countries like India and Pak are not doing too badly now.
from my personal experience, people go to india and pak to visit and invest there but despite huge demands from iraq, many companies are reluctant to even consider staring business there.