Sedevacantism, especially the kind that leads to ecclesiavacantism, most certainly poses some serious problems vis-a-vis the Church's indefectibility.

Sedeprivationism, IMO, addresses most of that quite nicely.

R&R clearly poses difficulties for indefectibility since it posits that the Church's Magisterium and Universal Discipline have effectively defected.  Indefectibility refers not only to the material Church, but also formally to the Church's mission.  It's not possible that the Church can defect in its MISSION of sanctifying souls and preserving the true faith.