What would be needed to make sure that Coptic Christian Egypt survives and remains mostly Coptic up to the modern day? What effects would this have on Northeastern Africa and the Middle East?
How does that prevent the Copts from being converted to Zoroastrianism and being Persianized in the coming centuries?A quick, decisive Sasanian victory in the Byzantine–Sasanian War of 602–628. Heraclius falling off his horse would help.
Byzantium tried over centuries; it didn't work. Why would whatever other empire be different?Whoever ruled would have converted them to their version.
Every state initially resists the religion it was imposed upon. Eventually,it might happen with different strategies. The popular belief of Zoroastrianism not being an evangelical belief is not completely right. Zoroastrians did convert other people in the past. You had Armenian,Kurdish,Afghan,Scythian,Sogdian,Kushan(India) people who were Zoroastrians apart from Parthians or Sassanians and so it isn't an ethnic religion. In India conversion isn't done due to historical reasons. And the rich Egypt would not be let away under any circumstances. They may do a more benign conversion by assimilating them and then today,they wouldn't be that distinct from Persians(Had Sassanid Empire shone only).Byzantium tried over centuries; it didn't work. Why would whatever other empire be different?
(Besides, I was under the impression Zoroastrianism wasn't an evangelical religion?)
You had Armenian,Kurdish,Afghan,Scythian,Sogdian,Kushan(India) people who were Zoroastrians apart from Parthians or Sassanians and so it isn't an ethnic religion.
How does that prevent the Copts from being converted to Zoroastrianism and being Persianized in the coming centuries?
Byzantium tried over centuries; it didn't work. Why would whatever other empire be different?
Besides, I was under the impression Zoroastrianism wasn't an evangelical religion?
Before the last Byzantine-Sasanian War, Miaphysitism was on the way out. They had agreed to ordain no more Miaphysite bishops. It was the Sasanians who set up a parallel Miaphysite church in Egypt independent of Constantinople.