Conquering Rome would deal a death blow to Christianity. All the other smaller ships that sail around the perimeter of Christianity are not strong enough to repel Islam by themselves.
That doesn’t mean that all believers will be gone, however, but the leadership of the Christian world would be in havoc.
It does for certain mean that 2000 years of Christian history will be destroyed almost imnediately. Destroying the history of something is similar to killing it entirely.
No, that’s why I mentioned the Reformation. The Roman Catholic church is not the totality of Christendom, nor Rome its epicenter.