Does it have to???
"… We do not claim that the collapse of Western civilization, and the transfer of the center of civilization to us [Islam] will happen in the next decade. Nevertheless [Western civilization] has begun to collapse and to become a pile of rubble."
That statement is pretty explicit to me. Or perhaps you believe the "transfer of the center of civilization" will happen through osmosis?
If anything, the statement implies that Western society will collapse on it's own, due to it's own values. I don't agree with the statement, but that's the point it seems to be making.