The partitioning of the nation seems to be the most sensible option should the national government continue to fail to stabilize the country.
This results in ethnic clensing and continued war. Probably open war between Turkey and the Kurds.
Sad thing is this is the longterm result regardless of what happens. This was the only possible result the minute we invaded. =(
The difference is that we carry it out now, in a peaceful manner, and leave enough U.S. troops behind to contain any possible conflict in the region (in a neutral zone, perhaps in southern Iraq where they could also distribute the oil revenues among the various emergent states).