There are quite a few passages from St Robert that at the very least should make us hesitate to declare a Pope 'ipso facto' deposed because we see 'manifest heresy' as some understand his fifth and 'true opinion', and that is all I want to establish. Of course, other theologians have other opinions also about heretic popes and whether they can be deposed, and the Church has tolerated all these opinions, for example Suarez, Billuart, John of St Thomas... but we have been through this so many times.

But here are a few considerations from St Robert that should at least make us hesitate before lopping off the Pope's head:

1. ...the Roman Pontiff cannot be deprived of his right to summon Councils and preside over them... unless he were first convicted by the legitimate judgement of a Council and is not the Supreme Pontiff. Moreover... the supreme prince, as long as he is not declared or judged to have legitimately been deprived of his rule, is always the supreme judge, even if he litigates with himself as a party - On The Church, Vol I, On Councils, Ch XXI

2. ...inferiors ought not be free from the obedience to superiors, unless first he were legitimately deposed or declared not to be a superior... Furthermore, it is impertinent because that oath does not take away the freedom of the bishops, which is necessary in Councils, for they swear they will be obedient to the supreme Pontiff, which is understood as long as he is Pope, and provided he commands these things which, according to God and the sacred canons he can command; but they do not swear that they are not going to say what they think in the Council, or that they are not going to depose him if they were to clearly prove that he is a heretic - Ibid

3. ...whether or not it is lawful for a Council to be summoned by anyone other than the Pope when the Pope should not summon it, for the reason that he is a heretic or schismatic... To the second and third, I respond... in those two cases an imperfect Council could be gathered which would suffice to provide for the Church from the head. For the Church, without a doubt, has the authority to provide for itself from the head... Hence, that imperfect Council can happen, if either it is summoned by the college of Cardinals, or the bishops themselves come together in a place of themselves - Ibid, Ch XIV

4. Two things can be considered on Bishops: Firstly, that they hold the place of Christ so for that reason we owe obedience to them... Secondly, that they might have the power of Order and Jurisdiction. If it is considered in the first mode, we are certain with an infallible certitude that these, whom we see, are our true Bishops and Pastors. For this, neither faith, nor the character of order, nor even legitimate election is required, but only that they be held for such by the Church... Now if this is considered in the second manner, we do not have any but a moral certitude that these will truly be Bishops, although it is certain with infallible certitude that at least some are true, otherwise God will have deserted the Church... - Ibid, On The Church Militant, Ch X

5. ...we cannot depose catholic bishops who have possessed their sees for so many centuries peacefully, unless they are legitimately judged and condemned; for in every controversy, the condition of the one possessing it is better... - Ibid, On The Marks of the Church, Ch VII

6. ...if the pastor is a bishop, they (the faithful) cannot depose him and put another in his place. For Our Lord and the Apostles only lay down that false prophets are not to be listened to by the people, and not that they depose them. And it is certain that the practice of the Church has always been that heretical bishops be deposed by bishop's councils, or by the Sovereign Pontiff...  - De Membris Ecclesiae, Lib I De Clericis, Cap 7 (Opera Omnia, Paris: Vives, 1870, pp 428-429). You will note that Bellarmine's proof from 'authority and reason' of his fifth opinion applies just the same to an heretical bishop. Manifest heresy renders you outside the Church whether you are a Pope, bishop, priest or layman. Yet the bishop is not ipso facto deposed?

7. ...jurisdiction is certainly given to the Pontiff by God, but with the agreement of men, as is obvious; because this man who beforehand was not Pope, has from men that he would begin to be Pope, THEREFORE, he is not removed by God unless it is through men. - On The Roman Pontiff, Bk II Ch XXX, second opinion

8. ...in the first place, it is proven with arguments from authority, and from reason, that the manifest heretic is “ipso facto” deposed. The argument from authority is based on Saint Paul, who orders that the heretic be avoided after two warnings, that is, after showing himself to be manifestly obstinate - Ibid, fourth opinion

Father Chazal leans toward the Cajetan / John of St. Thomas position, or, rather some synthesis of the two, since they're not identical.  He opens one of his talks by saying that the sedevacantists seem to hold that only St. Robert's opinion is legitimate, but the Church has not ruled on the matter.  He does have a point.

He comes up with a position that ends up being very similar to sedeprivationism, and the one towards which I myself lean, in theory.  In practice, I don't believe these V2 papal claimants had even material claim to the papacy, because I am convinced of the so-called "Siri Theory".

While he's never addressed that old munus thing, I would imagine he's say yes, that he has the munus, the office, but is incapable of exercising it due to manifest heresy.

No, according to Canon 2263, an ipso facto excommunicate (while in that state) is "removed from legitimate ecclesiastical acts." Meaning a Pope is not a "legitimate authority" while in a state of ipso facto excommunication.

But his acts while in that excommunicated state could, in theory, become valid later if and only if he were to repent of his errors before he was formally condemned (Level 3 excommunication). So his "acts" are suspended awaiting resolution of the problem. In the meantime, we have no obligation to follow an ipso facto excommunicates dictates. Rather, we should ignore them.

Of course, none of this applies to Bergoglio because he was not lawfully elected anyway, according to UDG. He is simply a usurper and should be expelled.