My scenerio - Imagine that instead of becoming the absolute ruler of Arabia, Muhammad dies during the battle of Uhud (in reality he almost died). His army, demoralized after the death of the prophet, disintegrates and suffers massive casualties. The remaining believers fell into captivity, bitterly disillusioned. Some of them revert back into their previous religions, some of them remain Muslims but they don't play a prominent political role. After a handful generations the new religion dies a natural death. The world never hears of Islam.
What would be consequences of Islam-less Middle East in 100? 200? 1000 years? How could the Middle East look today? What about Europe without Muslim influence but with a strong Byzantium as a neighboor?