Z's dead, baby. But Osama bin Laden (OBL) remains alive.
Nowadays, we don't hear from OBL much - but evidence overwhelmingly suggests he is still alive. Alive, OBL still poses an immense threat to the security of the United States. The threat is not neccessarily from another personally-orchestrated massive attack upon US soil, but rather the rallying effect that OBL has upon rank and file jihadis worldwide. It is unlikely in fact that OBL has any direct operational control over Al Qaeda - the latter organization now more of a "version 3.0" distributed entity rather than a coherent hierarchical chain of command.
OBL's primary influence comes from his fatwa (pronouncements). Traditionally, a fatwa has simply been a ruling on a religious matter - an interpretation of fiqh. A believer who has a question on religious interpretation or action would go to the ulema (learned scholars or local religious authorities) and present their case; the ulema would render an opinion after consultation with the Qur'an and those hadith which their School considered valid.
In the time of the Prophet SAW of course there were no schools of thought, only Islam - hence any pronouncement by the Prophet was a fatwa by definition. Likewise, the various Caliphs and Sultans and Mughals and whatnot also issued fatwa that applied to their subjects, because their authority was religious as well as political. In modern times, with the exception of Iran, no Islamic government claims religious authority and hence they do not issue fatwas (though certainly they compel their citizens through other means).
So how then can OBL claim such authority? Into the vacuum left by secular (tyrannical, to be sure) governments, stepped any charlatan with the desire to reshape Islam. Syed Qutb was that charlatan, and Bill Allison of now-defunct Ideofact blog did truly yeoman's work in deconstructing Qutb's writings. OBL simply took Qutb's ideas further, and has adopted a kind of "caliph in exile" mantle. Dan Darling has termed this dynamic "Magneto appeal".
The bottom line is that OBL has no authority to issue fatwa other than that granted to him by muslims themselves. To combat him, therefore, requires a systematic de-legitimization of OBL as an authority. I undertook one such de-legitimization a few years ago.