From what I can see, al-Qaeda is done for. The celebrity is gone. The leadership is being killed off too quickly for them to find adequate replacements — for instance, of the three guys under Khalid Sheikh Mohammed, two of them were already killed when he was captured. Now, the US government might have their hands on everything al-Qaeda has been planning.
The death of Osama probably will inspire people to join terrorist organizations, especially among populations of people who are disenfranchised and impoverished (that is why al-Qaeda sent agents in 2009 to Somalia and Yemen to assist regional terrorist organizations in training recruits). I doubt they would join the al-Qaeda network since now it is common knowledge that the US military has scored a substantial amount of intelligence on the organization.
Perhaps more importantly, people will be averse to joining al-Qaeda because the unifying message of Osama will be overwritten by the divisive persona of Zawahiri, who will likely be taking Osama’s place as emir. This is a guy who has branded the Muslim Brotherhood as heretical, and not the Egyptian Muslim Brotherhood specifically as far as I can tell, who sound more like Republicans if they were in Northern Africa, but rather all organizations that call themselves the Muslim Brotherhood, which covers a lot of gorund.
So, in all likelihood, the people who would join al-Qaeda will be distributing themselves among smaller, regional terrorist networks. I highly doubt that there will be another terrorist network starting up anytime soon that will have the same global presence that al-Qaeda has had. One reason why al-Qaeda managed to develop such a presence was through Osama, who was already something of a war hero in the Middle East for leaving the comforts of upper-class living in Saudi Arabia to fight the godless Soviets in Afghanistan alongside the Mujahideen. I am not sure if there is anyone else with that kind of reputation in the Middle East and Northern Africa, someone with a sort of legendary status that people can get behind.
Thus, what I think is most likely in the near future is that there will be increased membership in smaller, regional terrorist organizations. No one organization will see such a significant rise in membership that they will be able to develop much influence outside of their region. There probably will not be some legendary war hero with a unifying message that people can get behind for years. Each network lacking the ability and drive to cooperate with other groups and not having the influence of numbers nor fundraising power of a celebrity presence, it will be quite some time before any terrorist network will be able to coordinate attacks such as on New York, London, and Madrid.
Consequently, the bad news is that if the terrorist networks can’t pull feasible plans together to attack outside of the Greater Middle East, then they will settle for attacks within the Greater Middle East. There will be more attacks like the one in Marrakesh, more embasy bombings, more attacks on foreign troops occupying their territories.