They’re not even taking over Africa. There the fastest-growing religion is evangelical Christianity. When the African Christians decide to move north into Europe for work and opportunity, it will inject some energy into a dying civilization.
You will note a distinct lack of anything approaching the grandure of the great cathedrals, the beauty of Paris, Milan, Florence, Warsaw, Berlin and the other great European cities, the art of Michalangelo the great philosophers and writers of the west, the scientists who have invented the modern world flowing out of Kenya, the Congo and Nigeria!
It is far more likely that a flood of central Africans into Europe would result in human sacrafice, albinos being used for witch doctor medicine, gang warefare and mass amputations, rampant rape and polygamy and other cultural markers of African presence than that Europe could be saved.
The idea that Christianity can somehow transform low intelligence tribal people into Flemish and Dutch literate merchants is silly.