What would be the best case scenario for Islam?
My guess would be a successful push into France, an early capture of Constantinople, and now you have Islam in control of most of Europe. After Constantinople, there was just tribal societies and such (Bulgarian Empire could prove to be a challenge). And with France in their hands and the Balkans in their hand, Italy would fall quickly, and soon the Muslims will be able to discover the New World.
My guess would be a successful push into France, an early capture of Constantinople, and now you have Islam in control of most of Europe. After Constantinople, there was just tribal societies and such (Bulgarian Empire could prove to be a challenge). And with France in their hands and the Balkans in their hand, Italy would fall quickly, and soon the Muslims will be able to discover the New World.