Defeating ISIS is simple (in theory)
The strategy is simple and consists of two prongs. As the British did in Kenya during the Mau Mau uprising, ISIS must be made unfashionable (a quote from one of the British generals fighting the Mau Mau was that it was his goal to make it unfashionable to join) in the eyes of moderate Muslims. With the burning of the Jordanian pilot, ISIS is well on it's way to occupying that moral low ground. More lay and religious Muslim leaders are speaking out against the group.
Military action goes hand in hand with showing ISIS's essentially anti-Muslim behavior. Inflicting a series of military defeats on the group will serve to dissuade more young men searching for an identity from joining. After all, as bin Laden noted, who would choose a weak horse to ride?
Thankfully, this is also underway. ISIS holds a great deal of land, but is unable to control it. Territorial shrinkage is a given when its enemies press in from several directions, as is happening.
Although their military defeat is a near certainty -- especially if Iran or Turkey become involved, ISIS can only be extinguished by Muslims turning away from it. Making the group and its violence unfashionable can do this.