It can be argued whether error or heresy leads to the loss of faith and immorality, which is most often (but not always) what I believe is the case, or whether it's the other way around.
I judge men by their fruits, for fathers, their fruits are their children and how they turnout, for priests it is their faithful and how they turn out. I've seen expert book writers and lecturers in subjects like sedevacantes, Jews, NWO etc. that have been a disaster as fathers, spending all their time on their subject. It's like the saying, "the shoemakers children have holes in their shoes". The shoemaker spending all his time working on other peoples shoes and not on his family. Really, it is like straining gnats and swallowing camels.
To me, the details how a Vatican II pope can be or can't be a heretic and is or isn't a true a pope, is not something that anyone will ever conclude with absolute certainty, for it is an unprecedented situation. If the whole world goes to pot, while I do my job raising my children to LIVE the faith, to be examples to others, the question of sedevacantes will be as nothing.
P.S. - I'm of the thinking that that love of sin leads to loss of the faith (heresy, blindness of faith, apostacy.)