Arab warriors invaded Egypt, propagating Islam to the Egyptians, especially those who lived in the lower and middle parts of the country. The difference is that the Egyptian tongue remained the language spoken by most of the population, (which means "Coptic" is just another phase in the history of Egyptian language in this scenario) and its status became more prominent and prestigious thanks to epics "The Tale of Kemet", compiled and written by Iraqi-born Ibn Wahshiyya and a retelling of "Tales of the Kings of Kemet" in Egypto-Arabic script. In effect, this alternate Egypt is another counterpart of Persia/Iran, with a little bit of difference: predominantly Muslim, speaking it own language, but with a sizable Coptic (and Christian in general) minority.