Problem is, There are another Jihadi John's to replace him.
The way we have sat back and done nothing (or even encouraged) while IS has set up its Caphilate is in itself a major failing of the west.
They are fighting Assad, so we have done nothing to halt them. ISIS's weapons are American, and we are supposed to believe that is an accident. The Saudis bankroll them. ISIS make $millions a day from Iraqi oil which is uses to buy weapons. Why has that trade not been closed down? To a large extent we have aided and abeted ISIS and now it is coming back to haunt us.