That has an interesting impact on world history. Fast forward a few centuries and Muslim explorers discover the Americas. The upshot appears to be that Christianity ends up as a footnote to history, an obscure cult that died out in the early middle ages and isn't missed by anyone.
On the other hand, since Jesus is a Prophet in Islam and Muslims revere him as a messenger of God, plus the fact that the Quran mentions Jesus more times than it mentions Muhammad, and you can see that Jesus' legacy is very much still alive, just in an Islamic form.