From what i understand, having done some research on Arabia, the pagan goddesses Al-Uzza, Al-Lat and Manat were becoming increasing overly revered in Arabia, and soon enough they were starting to encompass all the domains of the other minor gods. It seems that much like Judaism, Arabian paganism was dropping the other gods in favor of these three deities, and Muhammad himself is said to have credited the strength of this trinity during the conquests of Arabia. Should Muhammad not arise, then a unified Arabic paganism centered around Al-Uzza, Al-Lat and Manat would probably arise, and dominate Arabia, perhaps barring Judaistic Yemen. With the population boom in Arabia, the people would eventually try to expand out of the interior, and we could have an Arabic pagan Iraq and Syria, and even Egypt, if they are lucky. There have also been rumors that 'Allah' as a god did exist in arabic paganism, however in a much diverse sense. So really while Islam may not explode and become a thing, other religions coming from Arabia may explode alongside the arabic population boom and conquer a good amount of territory, especially after the Rhoman-Iranic exhaustion.