With the death of bin Laden, the central organizing ideology that presented an existential seduction to the Muslim world and an existential threat to the Western world is damaged beyond repair. We’re left with free-lance terrorists who will, of course, be able to inflict some harm. But the Somali pirates are able to inflict harm on civilians, and that doesn’t turn them into an existential threat to the Western world. That existential threat is gone.
But al-Qaeda was never an "existential threat" to the West. Al-Qaeda was a challenger in the Middle East, but the Arab world in general does not have enough economic, scientific, military, or any other kind of power to pose an "existential threat" to the U. S. and Western Europe. The 9-11 attack was a spectacular success for al-Qaeda, but it didn't change the balance of power between the U. S. and al-Qaeda in any way. The American economic and military apparatus wasn't damaged in any substantive way. As a result, the U. S. was able to flex its muscles, unleash a wave of repression, break up most of the al-Qaeda apparatus, and begin a hunt for Osama bin Laden that was always going to end in bin Laden's death.
With bin Laden's death, it is likely that the al-Qaeda organization will be finished and that "al-Qaeda" will be mostly a name adapted by small terrorist organizations to honor themselves with the association with 9-11.
But al-Qaeda was never anything but active at the margins of the global political system.