I know that people criticize SVism of over 60 years, but even having a dysfunctional hierarchy for that long is just as much a problem as having none.
Having a dysfunctional hierarchy still leaves a possibility for a future conclave, and pope, to judge the the heresiarch who held office. Going the route of some sedevecantist positions (I'm not saying this is you, necessarily) would leave even that route out of the question. Hence your appeal to Sts. Peter and Paul prophecy (reminds me of the BODer appeal to an angel baptizing someone if they truly wanted unity with the Church). I mean, how many of those "hardline" sedevecantists would accept +Vigano's calling out Francis and electing another pope- even if it were done? Not many, I'd guess.