When do heretics depart...?

When does a heretical organization cease to be the Church? It seems wrong to think that some action or statement of a heretical nature automatically places an organization outside the Church and deprives it of the grace of the sacraments. The community ceases to be the Church not so much by virtue of a formal and external act, as by virtue of the general condition of ecclesiality in a given organization, expressed in a set of manifestations which, in turn, fall under the specific prohibitions of anathemas, canons, etc., on the basis of which one can speak of the unecclesial nature [netserkovnosti, нецерковности] of the community; but this general condition in a given organization, once part of the Church, does not come immediately, but gradually (the opposite understanding has been called the "switch theory"). It is precisely this general condition that is primary; its consequence is a situation in which specific heretical statements and actions of the hierarchs are not sufficiently counteracted by the flock; then the organization in question can be considered outside the Church. It is also important to keep in mind that in a community that has fallen away from the Church, each member [prior to a formal verdict by the Church] has a different "relationship" with the efficacy of the grace of the sacraments, depending on his orientation toward the true Church (which depends on many different factors - ignorance of the true situation, the general level of Church culture, etc.). The fact that the transitional period in terms of falling away from the Church in a certain community can last quite a long time is also testified to by examples of people who are honored by the Church as saints, while they remained and rested in a particular heretical community (or rather, in a community in transition which ended in its falling away) - in particular, St. Constantine the Great, St. Isaac the Syrian, and the Amorite Martyrs.

-  Book of Heretics [in Russian], by D.S. Biryukov, St. Petersburg, 2011, excerpt from the Foreword.