I doubt that the Arabs will be as sucessful without Islam
Islam is an unifiing concept, without each city /tribe has its own (though) related faith and philosophy.
Even if the Arabs unite (probably much later) without Islam the unifying element for the other cultures disappears.
At "worst" Arab conquerors will for the ruling caste of different kingdoms and the "commoners" will keep their culture - as it happened so often in history.
Islam is an unifiing concept, without each city /tribe has its own (though) related faith and philosophy.
Even if the Arabs unite (probably much later) without Islam the unifying element for the other cultures disappears.
At "worst" Arab conquerors will for the ruling caste of different kingdoms and the "commoners" will keep their culture - as it happened so often in history.