Call me "ultra-traditionalist," but these are some more quotes I found:
"Be not deceived, my brethren: If anyone follows a maker of schism [i.e., is a schismatic], he does not inherit the kingdom of God; if anyone walks in strange doctrine [i.e., is a heretic], he has no part in the passion [of Christ]. Take care, then, to use one Eucharist, so that whatever you do, you do according to God: For there is one flesh of our Lord Jesus Christ, and one cup in the union of his blood; one altar, as there is one bishop, with the presbytery and my fellow servants, the deacons"-St. Ignatius of Antioch, Letter to the Philadelphians 3:34:1.
"Whoever is separated from the Church and is joined to an adulteress [a schismatic church] 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."-St. Cyprian of Carthage, The Unity of the Catholic Church.
"Let them not think that the way of life or salvation exists for them, if they have refused to obey the bishops and priests, since the Lord says in the book of Deuteronomy: And any man who has the insolence to refuse to listen to the priest or judge, whoever he may be in those days, that man shall die [Deut. 17:12]. And then, indeed, they were killed with the sword...but now the proud and insolent are killed with the sword of the Spirit, when they are cast out from the Church. For they cannot live outside, since there is only one house of God, and there can be no salvation for anyone except in the Church."-St. Cyprian of Carthage, Letters 61[4]:4.
"When we say, Do you believe in eternal life and the remission of sins through the holy Church? we mean that remission of sins is not granted except in the Church."-St. Cyprian of Carthage, ibid., 69[70]:2.
"Peter himself, showing and vindicating the unity, has commanded and warned us that we cannot be saved except by the one only baptism of the one Church. He says, In the ark of Noah a few, that is, eight souls, were saved by water. Similarly, baptism will in like manner save you [1 Peter 3:20-21]. In how short and spiritual a summary has he set forth the sacrament of unity! In that baptism of the world in which its ancient wickedness was washed away, he who was not in the ark of Noah could not be saved by water. Likewise, neither can he be saved by baptism who has not been baptized in the Church which is established in the unity of the Lord according to the sacrament of the one ark."-St. Cyprian of Carthage, ibid., 73[71]:11.
"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."-St. Cyprian of Carthage, Treatise on Rebaptism.
"It is, therefore, the Catholic Church alone which retains true worship. This is the fountain of truth; this, the domicile of faith; this, the temple of God. Whoever does not enter there or whoever does not go out from there, he is a stranger to the hope of life and salvation...Because, however, all the various groups of heretics are confident that they are the Christians and think that theirs is the Catholic Church, let it be known that this is the true Church, in which there is confession and penance and which takes a health-promoting care of the sins and wounds to which the weak flesh is subject."-Lactantius, Divine Institutes 4:30:1113.
"Just as baptism is of no profit to the man who renounces the world in words and not in deeds, so it is of no profit to him who is baptized in heresy or schism; but each of them, when he amends his ways, begins to receive profit from that which before was not profitable, but was yet already in him."-St. Augustine, On Baptism, Against the Donatists 4:4[6].
"I do not hesitate to put the Catholic catechumen, burning with divine love, before a baptized heretic. Even within the Catholic Church herself we put the good catechumen ahead of the wicked baptized person...For Cornelius, even before his baptism, was filled up with the Holy Spirit [Acts 10:4448], while Simon Magus, even after his baptism, was puffed up with an unclean spirit [Acts 8:1319]."-St. Augustine, ibid., 4:21[28].
"Whoever is separated from this Catholic Church, by this single sin of being separated from the unity of Christ, no matter how estimable a life he may imagine he is living, shall not have life, but the wrath of God rests upon him."-St. Augustine, ibid., 141:5.
"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 [and remains in deliberate schism]. He must therefore return to the Church, not so that he might receive again the sacrament of baptism, which no one dare repeat in any baptized person, but so that he may receive eternal life in Catholic society, for the obtaining of which no one is suited who, even with the sacrament of baptism, remains estranged from the Catholic Church."-St. Fulgentius of Ruspe, The Rule of Faith 43.
I don't know, these seems fairly explicit.