Seriously, the complete destruction by nuclear bomb of Mecca may be just the thing to destroy Islam.
After all, Muslims believe nothing happens without being the “Will of Allah” therefore, if Mecca were to disappear in a mushroom cloud one fine morning, it could only be because Allah willed that Islam and a belief in Allah disappear from the face of the earth.
We do know that the A-Bomb ended the Japanese belief in the Emperor as the living god of Shinto, thus the H-Bomb could end the belief of billions in the myth of Allah.
The film is set in the far future. Mankind has colonized the stars. On one planet one of the people who helps Riddick is a Muslim. In part of the dialog, the Muslim explains why there still IS an Islam. Supposedly, someone DID nuke Mecca in the past. The Muslim explains that when the mushroom cloud rose into the sky, "the ashes of Mecca were now carried around the whole earth, so now the whole Earth is considered a holy place".
Those who practice Islam, loony as they are, would find a way to justify the continued existence of Islam, despite the loss of their holiest city and center of worship.