The official catholic teaching is that a person who is a Catholic by virtue of having received the Sacraments of Baptism or Confirmation in the Church remains a Catholic unless or until he or she deliberately and voluntarily repudiates the Church. As a separate matter, a Catholic is bound by Canon Law
to follow with Christian obedience those things which the sacred pastors, inasmuch as they represent Christ, declare as teachers of the faith or establish as rulers of the Church. [Can. 212 §1.]
To the extent that they fail to comply, or deliberately violate that to which they are bound, they are in impaired communion with the rest of the church, but remain Catholics. A consequence of the impaired communion may be liability to certain penal consequences as laid out in the Code of Canon Law, and there are some consequences that have automatic consequences. Failing to accept, adhere to, and promote the Church's teaching on abortion, for example, carries the penalty of automatic self-excommunication by the individual. Ex-communication, however, simply bars a Catholic from all sacraments, except confession, but does not mean that the person is considered by the Church not to be a Catholic.
I am not sufficiently familiar with the writings of the Fathers to discuss which of them might have written on this matter, but in general my understanding is that most of the current teaching on this matter developed after the time of the Fathers, and thus, after the time of Scripture. Given my lack of knowledge of the Fathers on this matter, I welcome any who might be able to write definitively on this matter to edit this answer.