“It is impossible to stop something like this. I am glad they killed the guy. It tells all the other terrorists what their fate will be.”
You are right, but at the same time the problem is that the “other terrorists” DON’T CARE if they are killed. Their whacked-out religion has short circuited their instinct for self preservation. They welcome death. The only way to deal with this kind of insanity is to wipe out the entire sect, all genders and ages. In India they had to deal harshly with the cult of Kali in the nineteenth century, but in this day and age it won’t happen.
Some terrorists do care if they die. One of the killers of the Paris attack ran away and did not blow himself up because he chickened out.