You can't destroy Islam, any more than Islam can destroy Christianity.
What Usama bin Laden and the Wahhabis are trying to do, is to get the West to do something like striking at Mecca, or Medina...it will in effect unite all of Islam under their banner, creating what Islam has lacked since the times of the Prophet.
Usama and the Wahhabis want to create a Caliphate, a Wahhabi Caliphate, and a united Islam.