Why do you think they will destroy the tomb?
The Caliph has said he would destroy the tombs and tear down the Kaaba itself. His brand if Islam is a radical departure from the excepted view of this religion. He is trying to “Purify” Islam of these “pagan” ideas. Kinda like the Pilgrims wanted to purify the Christian Church and rid it of Roman Catholic elements—Like Christmas! It would be good to have them roll into Mecca and purify the place.