But Father also goes on to say that the same thing would happen even if NONE of them had been legitimate, due to "color of title". So I hold that the material popes can continue to have a pass-through jurisdiction to the bishops based on color of title.
The sede-privationist theory is the best attempt to try and "save" sede-vacantism, I agree. If I were forced to be a sede, I would probably hold something like it. Bp. Guerard correctly perceived that what many of the sedes of his day were saying, that none of the Cardinals, Roman clergy appointed by the recent Popes were even Cardinals or Roman clergy, would lead to the Church defecting.
With regard to the above, I would say, Jurisdiction could be supplied by Christ to a Catholic Anti-Pope. But it seems unlikely that it would be supplied to a non-Catholic manifest heretic, as for e.g. cuм Ex says those appointed by such will lack any authority. Fr. Gueranger, speaking of early sees that lost the Roman Catholic Faith, says they lost with this, the power to appoint Bishops as well.
cuм Ex: "
each and all of their words, deeds, actions and
enactments, howsoever made, and anything whatsoever to which these may give rise, shall be
without force and shall grant no stability whatsoever nor any right to anyone;"
Archbishop Lefebvre: "They (the sedevacantists) argue further that, chosen by a heretical Pope, the great majority of the cardinals are not cardinals at all and thus lacked the authority to elect another Pope. Pope John Paul I and Pope John Paul II were thus, they say, illegitimately elected. They continue that it is inadmissible to pray for a pope who is not Pope or to have any "conversations" (like mine of November 1978 with one who has no right to the Chair of Peter"
Fr. Gueranger: "By God's permission, the Sees of Alexandria, Antioch, Constantinople, and Jerusalem, were defiled by heresy; they became Chairs of pestilence (Ps, i. 1); and, having corrupted the faith they received from Rome, they could not transmit to others the mission they themselves had forfeited."
Canon 4 of the Eighth Ecuмenical Council applies this to the schismatic intruder Photius, saying those elevated by him, are not really elevated: "We declare that Photius never was bishop [i.e. patriarch] nor is now and that those ordained or promoted by him may not retain the dignity to which he raised them"
https://sourcebooks.fordham.edu/basis/const4.asp