Destroying Mecca would destroy Islam as we know it, but it would not destroy the hundreds of millions of surviving Muslims enraged and mobilized by such an act.
OTOH, Judaism survives quite well without a High Priest, a Temple, and an Altar with daily burnt offerings. Islam would adapt to the destruction of their holiest of places also.
OTOOH, it is a fun fantasy to contemplate from time to time.
See my #37 and #39.