Following the first post a rapid assessment by ICSR and a short "taster":
Awlaki’s role in al-Qaeda and, more generally, within the global jihad movement was principally as an ideological cheerleader. He was not an operational commander in the way that Osama bin Laden or Atiyah Adbul-Rahman were, and will not therefore require direct replacement.

Few English speaking preachers have the same background and following that Awlaki enjoyed over the last decade, and it is therefore unlikely that a comparable replacement will emerge.
Link:http://icsr.info/publications/newsle...thofAwlaki.pdf