Iraq Civil War?

After eight years and over a trillion dollars later, President Obama has announced that US all US troops will be pulled out of Iraq by mid- December. While Obama had promised in his campaign to bring the troops home, it is still being seen by some (Senator John McCain and others) as partly a failure on the part of the Obama administration. It was seen as the intention of the US to leave some troops in Iraq to continue with training of Iraqi security forces and to help keep the country secure instead of a full withdrawal. This is not happening according to them because of the Obama’s administrations failure to negotiate immunity from Iraqi law for US troops.
While the US public is weary of the Iraq War and the US is no longer in a position to afford to continue its involvement at its current level, one must wonder how ready Iraq is to go it alone. With anti-American cleric Muqtada Al-Sadr waiting in the wings, how long after the US pullout will he wait to attempt to overthrow the government of Iraq? Will we see a civil war in Iraq in the new year?
Al-Sadr, an extremely popular figure in Iraq, has close ties with Iran. It is not certain whether the present government of Iraq could withstand a Sunni/Shia civil war. But it is almost a sure thing that if a Sunni/Shia civil war should breakout, that Iran would be involved, either in instigating or in supporting it. It would definitely not be in the US interest to have an Iran friendly regime in the region, but it is not certain whether the US government is willing or able to send troops back into Iraq, let alone gaining public support.
However, the US could support Iraq by sending a small number of Special Forces troops, as well as extending the use of drones in the area to support Iraqi government troops. While an Iranian supported civil war in Iraq could possibly distract Iran from its nuclear program, if this scenario were to play out, with Iran supporting a fighters in Iraq and the US supplying Iraq with enough military aid to not lose, it would bring us close to the days of the Iran/Iraq war, with shades of the Cold War, by having the US fighting a proxy war with Iran in Iraq. As bad as this sounds, would it be worse than having an Iran friendly government in the Middle East, or in the end as bad as keeping a few troops in Iraq without immunity?