It seems a great deal of the fathers beleived there is no salvation outside the One True Church.
"Whoever is separated from the Church and is joined to an adulteress is separated from the promises of the Church, nor will he that forsakes the Church of Christ attain to the rewards of Christ. He is an alien, a worldling, and an enemy. He cannot have God for his Father who has not the Church for his mother" (251 AD)
"Outside the Church there is no Holy Spirit, sound faith moreover cannot exist, not alone among heretics, but even among those who are established in schism" . (256 AD)
--St Cyprian, honored in Coptic, Greek, Syrian, and Latin Churches
"We believe also in the holy Church, that is, the Catholic Church. For heretics violate the faith itself by a false opinion about God; schismatics, however, withdraw from fraternal love by hostile separations, although they believe the same things we do. Consequently, neither heretics nor schismatics belong to the Catholic Church; not heretics, because the Church loves God; and not schismatics, because the Church loves neighbor" (393 AD)
--St Augustine, honored in Coptic, Greek, Syrian, and Latin Churches
"Anyone who receives the sacrament of baptism, whether in the Catholic Church or in a heretical or schismatic one, receives the whole sacrament; but salvation, which is the strength of the sacrament, he will not have, if he has had the sacrament outside the Catholic Church. (524 AD)
--St Fulgentius, honored in Greek and Latin Churches
And there are countless other sayings of the fathers which state that there can be no salvation in a schismatic church, that is, one that is excommunicated from the One True Church, (commonly refered to by the fathers as the "Catholic Church.") By this definition, if the Coptic church is that "Catholic Church" that they talk about, then there is no hope of salvation even in the Eastern Orthodox Church. Indeed, a very large amount of Eastern Orthodox bishops consider us heretics and believe there is no salvation in our church. Many Latins feel the same way.
However, some will argue that those who are not "visibly" inside the true church, may be inside "invisibly," and thus have salvation. By this logic, I would think that those who are not "visibly" baptized or "visibly" receive Eucharist, or "visibly" beleive in Jesus Christ should also salvation: Muslims, Jews, Atheists, Protestants, Pagans, etc. Certainly this cannot be right! You must be "visibly" in the One True Church to have salvation.
My question is, why do you think the Oriental Orthodox Church is that One True Catholic Church? What makes you so sure that this is the True Church and the Eastern Orthodox Church is not?