It is happening already. The fighters of ISIS are deserting, and leaving the area to join a different group. There is too much resistance from the world for ISIS to continue thriving. ISIS has shown strong military force in many areas of Syria. However, the areas they have captured are slowly being recaptured by opposing sides. The US has contributed to the overhaul by its use or air strikes.
The U.S. can fight ISIS all they want, but it's already a bigger problem than anyone would ever want. Someone once said that, although Osama Bin Laden is dead, there are new Bin Ladens born every day in Islamic countries. Too many wars, too many dead people will forever stay with people in those countries.
While it is an important first step, the set up of two U.S. air bases in northern Syria is a far cry from the answer to the complete problem of ISIS. ISIS is a deeply embedded and intricate problem. In my opinion, Americans still are not aware of the full extent of their power and terror. It is going to be a long, violent and horrific process to try and snuff out ISIS altogether.
ISIS is working on the premise that the West is evil. Its members will fight guerrilla-style until they are all dead or we leave. The answer is to keep ISIS from spreading by isolating the group from potential new recruits. Education and compassion for the people in the Middle East is the answer. The military is only the key to further problems there.