Having said that, I think the opinion that a pope would remain pope if a heretic is wrong. That indeed would be papolatry - ironically for Stubborn. Because then a man would be elevated above divine dogma, above truth itself.
Well, it's all intertwined with the thorny question of when heresy has been sufficiently discerned.
Scenario 1:Sedevacantist: "JP2, you're a heretic."
JP2: "No I'm not. My position is consistent with Tradition when you apply the proper hermeneutic." [not yet a heretic]
Church: "We've studied your position and consider it heretical." [not yet a heretic]
JP2: "I disagree." [not yet a heretic]
Church: "We definitively declare that your position is heretical. You must retract it." [not yet a heretic]
JP2: "I retract it." [not a heretic]
OR
JP2: "I stand by it." [heretic] -- IPSO FACTO DEPOSED ... as per the Bellarmine position.
OR
Church: "We declare that JP2 is a heretic and it outside the Church; we no longer recognize him as pope." -- DEPOSED DECLARATIVELY BY CHURCH ... as per Cajetan & John of St. Thomas
Scenario 2:JP2: "I know that the Church teaches [a dogma]. But I don't believe it anyway." -- IPSO FACTO DEPOSED ... as per the Bellarmine position
[but how often does THIS happen]
Scenario 3:JP2: "I don't believe in Catholicism anymore. I've decided to become a Buddhist." -- IPSO FACTO DEPOSED ... as per the Bellarmine position
[again very unlikely]
Scenario 4:Joe Catholic: "JP2 is a heretic." [no longer Pope ... according to many SVs]
Scenario 5:JP2 says something heretical. [still the Pope]
JP2 says: "oops, I simply mis-spoke ... stumbled over my words." [still the pope]
In Scenario 1, by far the most common, at some point the Church must discern the heresy and discern that the Pope is guilty of heresy.Unfortunately, most SVs think that it works like Scenario 4. That's why you have some SVs declaring Pius XII and even Pius IX non-popes.
Also, look at Scenario 5. Obviously if someone says a materially heretical thing, he doesn't instantly get deposed. It could have been a mere stumble over the words. Take it another step. The words were deliberate, but JP2 in his confusion had an incorrect understanding of the terms involved and didn't intend heresy. Take it to the next step. JP2 understood the terms involved but really thought that his proposition was orthodox. Then someone [the Church] needs to call him on it. If he retracts immediately, then it's obvious that there was never any pertinacity there. So at what point, when someone insists that his propositions are orthodox, does the actual HERESY become "manifest"? I submit that it's only when the Church calls him on it and he refuses to recant ANYWAY that the pertinacity of his belief becomes manifest. It's not merely when the objectively heretical proposition was uttered. And this manifestation doesn't happen without the Church's DISCERNMENT.
So this question is FAR from as simple as most sedevacantists make it out to be, according to the old oversimplified syllogism:
MAJOR 1: Heretics are not members of the Church.
MAJOR 2: Non-Members of the Church cannot be Popes.
MINOR: JP2 uttered a heresy.
CONCLUSION: JP2 is not pope.