We cannot defeat ISIS or Al Qaeda by thinking of it as a government. Our outmoded strategy of killing the leader is a throwback to medieval times when capturing the enemy king meant you won. But each ISIS cell is more like a pirate crew. Their leaders are more like a pirate captain, answerable only to his crew and totally dependent on booty. They have no capacity to create what they need to function. Like pirates they are funded by what they steal "liberate, confiscate, commandeer". Killing a "leader" is just a promotional opportunity for the next in line to fight over.
To fight they need to steal ordinance. To defeat them they have to be deprived of everything they steal. Fortunately those things are easy targets. It is easy to hide a "sheikh" in a crowd, but where do you hide a tank or howitzer in the desert? If it is hidden, it is ineffective. The key to defeating them, which the Saudi's seem to understand is to destroy that which they love, hardware. The threat of death is no deterrent to those who think that to die in jihad is desirable.