I don't think Syria and Iran could stop the slide into chaos even if they wanted to. Syria isn't run by Sunnis in any event (Assad is an Alawaite, which is some Shia sect), so it is not like each side has a sponsor. So if the face saving exit strategy is to create some temporary reduction in the violence, while the US leaves, I doubt that will happen, and there will be no saving of face.
They are the oxygen that feeds the fire. Without, it may burn for a while only.
Iraq could have been a success- maybe- if immediately after the initial victory Iran and Syria and others has been put on notice. With a stick ready to be used on the violators.