Fr. Chazal held that Jorge Bergoglio was not ontologically pope. Therefore, he rejected Jorge Bergoglio as pope simpliciter. That he was "elected" by the cardinals is accidental. It would be up to the Church to formally declare the See vacant, but Fr. Chazal held the private judgment that Jorge Bergoglio was a public manifest formal heretic and therefore not a member of the Church. He didn't hold some wacko distinction between formally pope and materially pope. You, like Pax Vobis, take logical parts that are beings of reason and make them into real beings. Stop with your nonsense.
But how would that work, given that "the first See is judged by no one"?
An invalid Pope wouldn't be likely to say "okay, I'm busted, I'm not Pope after all". If he did, I have to think this would constitute a
de facto resignation, and thus the whole question of
sede vacante would disappear, the see would be manifestly vacant without question.