Iran will not tolerate a hostile, Sunni-dominated country on their western border. Too many Iranians died in the Iran/Iraq wars for them to allow the Sunnis to seize control again.
Look for a Sunni/Shiite civil war in Iraq, with Iran supporting the Shiites, and Saudi Arabia supporting the Sunnis.
Obama is a Sunni client, with Saudi Prince Al-Waleed bin Talal having greased the rails to get Obama into Harvard Law, so the US will take al-Queda's side with the Sunnis.
FWIW, my thoughts exactly. Add to that Russia siding with Iran/ISIL. Not pretty at all.