I think we are leaving advisers in small numbers
Isis went to Syria because Islamic muslims always run to areas in battle to die as it guarantees them their place in their Islamic heaven, and the only gurantee Islam teaches fro salvation...which they believe. ....Syria is Irans lynch pin to their Apocalyptic beliefs which is used by Irans leadership to motivate fighters to fight for 'political' asperations of the Iranian leadership. Without "religious' Islam they could not move any to fight for them..
So leave it tho them to sort out....but we have to protect the Kurds.