the only way to truly end the threat is to throw the ring of islam into the fires of mt. doom. since we can't do that, we can only play whack-a-mole, waiting for them to have their reformation and revelation of the truth that their prophet was a charlatan.
with ISIS it's easier than al-queada. while AQ had more complex highly sophisticated terror plots, ISIS gets its strength by the fact it is alive and has a physical presence and territory under its control. some muslims flock to that, and end up performing terrorism in their name because it appeals to them. destroy their claim to statehood, and end the problem. and yeah, then we just leave. if they show up again just do it again. this is what you do when you have termite infestation. you have defenses and take out any known hives. you set poison and traps but one day you still might end up with termites in the middle of your house again. kill them and find where they are coming from, kill that, and set up defenses again. what you can't do is kill all the termites in the world, even though that would end the problem. because even if we killed them all today, an idea is more insidious in its evil, which is why the entire ring must be thrown into the fire. or whack a mole.