Question:
"Does Killing Terrorist Leaders Make Any Difference?"
Answer:
No.
You pretty much have to kill ALL of them.
Edit:
Even that will work only for a short while.
In time, an entirely new crop of terrorists will spring from the well that generates them.
If you want to end jihadism, you have to destroy "the well" from which jihadis spring.
What -IS- that "well"?
C'mon, you know the answer.
If you don't, you'd better find out what it is pretty durn quickly!