It won't be chaos. A fundamentalist anti-western minority regime will quickly come to power.
Pull out and the whole region turns into a mix of north-korea and Iran and pretty soon you're paying more for fuel than for printer ink.
Really, there is no choice. US troops (and US casualties) in Iraq will be a reality for a very long time because the economy cannot withstand much higher oil prices.
But hey, Saddam is dead, right!