In my opinion, the two most likely conclusions are:

Option #1 A strongman will establish dictatorial rule over Iraq after a short but bloody civil war. This leader would take pains to NOT work with the Islamists and studiously avoid WMDs, thus undercutting support to oust the new ruler a la Saddam.

Option #2 Iraq will continue as it is on a macro level, but the three principal ethnic groups will end up in largely autonomous sub-states with their own armed militias. There will be a central government for UN interaction and certain civic projects, but it be left with only a token military and will function largely as a way to skim money off the top for the office holders. There will be constant "incidents" between the sectors, but nothing prolonged. Bagdad will be "neutral" territory for all and the most corrupt portion of the whole country.


Not at all sure which is more likely.