On an earlier thread, I was arguing with SeanJohnson, and I pointed out to him the fact that +Lefebvre was quite sympathetic to sedevacantism, but he denied it. After I produced the quotes, he stormed off the thread and then left CI for a time.
If even increasing numbers of people within the Novus Ordo are beginning to question whether or not Francis is a heretic, I think it's very unlikely that +Lefebvre would not have come out an open sedevacantist, with his one reservation being that only the Church can definitively settle the issue.
I don't know how +Lefebvre would reason through this, but I will say, while Francis certainly says more problematic things than his predecessors, he by pure happenstance seems to be better for trads who want to be in communion with him than JPII was. Mostly because he's too progressive to actually really want to force people to agree with him.
At this point the SSPX is PRACTICALLY regularized and Francis isn't seriously trying to persecute them.
To be clear this isn't a defense of the man, actually listening to his teaching would be dangerous, but he's not attempting to excommunicate anyone for not doing so.
Whereas John Paul II was actively suppressing the Latin Mass and actively only allowing it to people who were also OK with the Novus Ordo.
So I don't know how +Lefebvre would reason through that issue. For all I know he might be like "it actually doesn't matter anymore" or something (Sedevacantism, not Traditionalism.)
That said, I seriously doubt he'd bind sedevacantism on people, even if he did personally conclude that it seemed more likely.