That is a fatal misunderstanding of the roots and the leaders in Al Queda, and in similar groups. Osama, while not figured head, while quite a dominant and commanding presence was none of those things because of who he was, but because of what he said, what he was willing to do to put his beliefs into action, and who was willing to back him up with money.
There is no shortage of such individuals in Al Queda now, nor was there one in the past, nor will there be one in the future. I have no belief that 9/11 required Osama bin Laden alive at the time. It, or an equally bold and deadly event would have been achieved by Al Queda by that time if not soon thereafter, with or without Osama bin Laden.
Killing Osama will change nothing, in fact he is more valuable to us alive and required to fight us now, with us actively fighting back, in every WOT theatre in the world. Dead he would rise within radical Islam due to the near-myth status the west has created for him; because the world would see that his death changed nothing.
Well, who and how will they pick Osama's successor. It won't be easy to pick and it will be harder to enforce. He began this with his cash and publicity. Recruiting, money and support came to him as a person as much as the movement.
Despotic crowds have problems with leadership change.