No, Stubborn. When a heretic is elected, the election is null and void even if he has the "unanimous assent of all the Cardinals".
Your answer leaves the Church without a pope and without hope for one.
First, if possible, remember that the popes who made the law were non-sedevacantists. An argument can even be made saying those popes could be considered staunchly anti-sedevacantist if the term, as it is used today were around back then.
Your original answer that there is nothing to stop a heretic cardinal from being elected pope is based on PPX and PPXII's law - and is correct.
Yet here you are completely neglecting to take into consideration that same law of PPX and PPXII which lead you to conclude such a thing is possible in the first place. My guess is this is presumably because while you admit the outcome, you, as a sedevacantist, cannot possibly accept it without risking your SVism, as such, the only way out for you or any sedevacantist is to ignore the papal law completely and declare the election is null no matter what, based on a previous law or canon law.
Regardless of all that, this boils down to the fact that popes made a law that favors or risks that a heretic could be elected pope, but since such an election is null, the reason that the popes made the law, must have been just for the sake of going through the motions of a papal election for nothing. This is because "when a heretic is elected, the election is null", which means the election leaves the Church without a pope and without any hope for one.
The conclave disperses after they've accomplished their job of electing a new pope, the cardinals all go home satisfied with their election, yet the Church is left without a pope but the whole Catholic world is content that they have a newly elected pope - this is according to your two answers.
Is this correct?