The likes of +Lefebvre, +Fellay, +Sanborn, +McKenna, and the majority of Traditional bishops and priests have said and teach in their seminaries that people like Hindus and Muslims could be saved without having to profess the Faith, and without conversion before death or intending to receive Baptism, the ecclesiological implications of this fact is a time bomb ticking inside the entire traditionalist movement's arc.
Problem with that ecclesiology for a Traditional Catholic is that, if you hold it, you must say that there's no error in Vatican II and therefore no justification for the Traditional movement. That's why this belief that anyone can be saved without the need for belief in the Christ and the Holy Trinity, (nor a need for explict desire for baptism, nor baptism of blood, nor a perfect act of contrition). is THE burning issue for Traditional Catholics. If I accepted the ecclesiology held by most Traditional Catholics, I would be forced to renounce Traditional Catholicism and accept Vatican II. I could apply a hermeneutic of continuity to V2 that makes V2 look like Trent ... again, assuming their ecclesiology. This change was inevitable for the SSPX since they have been teaching "salvation without belief in the Incarnation and the Holy Trinity" for years in their seminaries.
So if these can be saved, it must mean that they are within the Church before they die. Consequently, the Church now consists not only of true actual Catholic members of the Church but also of various Protestants, Hindus, Muslims, etc. Now you clearly have subsistence ecclesiology, where the central visible core of the Church consists not only of the actual/public (and perhaps in voto) members while you have various invisible members, not co-extensive with the Body of the Church, who are yet within it ... to varying degrees. Now suddenly you have various degrees of partial communion with this subsistent core depending on how close doctrinally you might be (materially) to the fullness of Catholic doctrine. Now these are truly separated brethren, brethren because they are within the Church (if they can be saved) and separated because of their material separation from the visible Church. Now, when their intention to do the will of God itself pleases God and becomes salvific, since they have a right to please God and save their souls, they clearly have a right to follow their even erroneous consciences (since doing so pleases God and saves their soul).
It is incomprehensible how Traditional Catholics cannot see this ... except due to some cognitive dissonance on their part.
If this implicit-faith ecclesiology is tenable, then Vatican II does NOT teach error or heresy but simply adopts this opinion as that of the Church. Since when is adopting a probable opinion tantamount to heresy?