My own view is the problem is here for a long time because it has funding.
Initially funded by many sources (including Zestern powers) it is now self-sufficient through the sale of oil from captured oil fields. Hence the targetting of the refineries to reduce their income. No $ = no bullets, propoganda, food, etc, etc....
Militarily they are very vulnerable. Just one night of bombing raids from a small handul of aircraft has caused serious distruption to IS. Imagine a bombing campagne on the scale of Gulf War 1 or 2 followed up by soldiers to mop up the rest! The added bonus is that there is less grey with IS and less civilian population to hide amoungst so reduced collateral damage and greater tactical freedom.
So will they be around for long? I think not. Once the decision is made to properly intervene it will be very short-lived. The problem is that there are a number of elections due soon so expect intervention to be more forthcoming once they are done with (note: ours is next year!)