Well, according to some the post-Vatican II church (ie. the supposed Bark of St Peter) will do this...and yet there is not one prelate who appears to be Catholic/not Modernist. Yes, how will a bunch of Modernists/heretics declare one of their own a manifest heretic and non-pope?
So, yes, good questions. I'm not sure anyone has all the answers. I tend to think that this is up to God to sort out.
Doesn't Sacred Scripture already provide the action plan for responding to popes who attempt to promote error? "But when Cephas was come to Antioch, I withstood him to the face, because he was to be blamed" Gal 2:11
Was Cephas a manifest heretic? No. So, Scripture does not provide the action plan for the current crisis.
The sedevacantist movement appears to be essentially an unscriptural novelty which has arisen in response to other unscriptural novelties advanced within the "pastoral" Vat II documents.
First of all, "unscriptural" isn't normally the only standard a Catholic uses. Regardless, I would argue that the Great Western Schism was an "unscriptural novelty" as well. Never did Catholics believe nor think that the Church would ever have 3 "popes" vying for the Chair. Laity and clerics alike had to make judgments over who was the true pope until the Church settled the matter. Even Catholic saints made the wrong choice prior to that declaration.
So the "unscriptural novelty" argument against sedevacantism doesn't work.
But it's necessary to examine the logic behind all post-Vatican II novelties. There are wolves on every front in this spiritual war.
True. For me, it is not logical that a manifest, public heretic can possibly be the Vicar Of Christ and there is Catholic teaching to support it.
Hardly,
Saint Paul to the Galations 1:6-10
[6] I wonder that you are so soon removed from him that called you into the grace of Christ, unto another gospel. [7] Which is not another, only there are some that trouble you, and would pervert the gospel of Christ. [8] But though we, or an angel from heaven, preach a gospel to you besides that which we have preached to you, let him be anathema. [9] As we said before, so now I say again: If any one preach to you a gospel, besides that which you have received, let him be anathema.
Also it is not some newly applied novelty nor is it the sifting out of context of some document: IT IS THE STANDARD TEACHING OF THE CHURCH.
The quote by Saint Antoninus on the See being vacant in the event of heresy that I affixed last evening was cited in issuance of the Doctrine of Papal Infallibility at the Vatican Council of 1870.
"Ius Canonicum", the nine volume Canon Law compendium by Fr. Wernz, the Superior General of the Jesuits when they WERE Jesuits, is the most comprehensive reference available on Canon Law. Fr. Wernz died a few months before Pope Saint Pius X in 1914, and this edition from 1938 by Fr. Vidal, S.J. reflects as well the issuance of the Code of Canon Law in 1917.
If you are familiar with theological expositions, first are cited the possible theological positions and objections to a specific teaching, then are given the refutations of those objections and the sole correct position to be maintained and taught. This format is used by Saint Thomas Aquinas in the "Summa Theologica".
Jus Canonicum by the Rev F X Wernz S.J. and the Rev P Vidal S.J. (1938) Chapter VII
De Summo Pontifice
[The power of the Roman Pontiff ceases...]
453. By heresy which is notorious and openly made known. The Roman Pontiff should he fall into it is by that very fact even before any declaratory sentence of the Church deprived of his power of jurisdiction. Concerning this matter there are five Opinions of which the first denies the hypothesis upon which the entire question is based, namely that a Pope even as a private doctor can fall into heresy. This opinion although pious and probable cannot be said to be certain and common. For this reason the hypothesis is to be accepted and the question resolved.
A second opinion holds that the Roman Pontiff forfeits his power automatically even on account of occult heresy. This opinion is rightly said by Bellarmine to be based upon a false supposition, namely that even occult heretics are completely separated from the body of the Church... The third opinion thinks that the Roman Pontiff does not automatically forfeit his power and cannot be deprived of it by deposition even for manifest heresy. This assertion is very rightly said by Bellarmine to be "extremely improbable".
The fourth opinion, with Suarez, Cajetan and others, contends that a Pope is not automatically deposed even for manifest heresy, but that he can and must be deposed by at least a declaratory sentence of the crime. "Which opinion in my judgment is indefensible" as Bellarmine teaches.
Finally, there is the fifth opinion - that of Bellarmine himself - which was expressed initially and is rightly defended by Tanner and others as the best proven and the most common. For he who is no longer a member of the body of the Church, i.e. the Church as a visible society, cannot be the head of the Universal Church. But a Pope who fell into public heresy would cease by that very fact to be a member of the Church. Therefore he would also cease by that very fact to be the head of the Church.
Indeed, a publicly heretical Pope, who, by the commandment of Christ and the Apostle must even be avoided because of the danger to the Church, must be deprived of his power as almost all admit. But he cannot be deprived by a merely declaratory sentence...
Wherefore, it must be firmly stated that a heretical Roman Pontiff would by that very fact forfeit his power. Although a declaratory sentence of the crime which is not to be rejected in so far as it is merely declaratory would be such that the heretical Pope would not be judged, but would rather be shown to have been judged.