Pope Francis CANNOT lose "his Office" [UPDATE]

Over the past few days there have been reports of an historian speculating that Pope Francis can "lose his office", (but not be "deposed"), after he has been found "guilty" of "manifest" heresy. In other words he would materially cease to be pope, but not formally. 

Who would declare the Pope has lost his "office", and by what authority?

Who would decide what "manifest heresy" is, and by what authority? 

I refer readers to an article written a number of years ago by Br. Andre Marie, in which he wrote the following: 

Regarding the possibility of an heretical pope and his consequent loss of office, I would like to present another argument. Supposing we were to follow the opinions of certain authors that if a pope were to fall into heresy, he would then lose his office. Then suppose that we were to apply that opinion to a certain pope. At best, what we have accomplished is to establish, based upon theological speculation, the possibility that the See of Peter could be vacant. That is all we could do, given the uncertain nature of this situation. At this point, the individual Catholic is at a moral juncture: Either accept a man as the Roman Pontiff whom he thinks might not be pope, or reject him. If he realizes that the claimant to the Apostolic See might be the pope — and he has to admit that he might be — then rejecting the claimant constitutes a schismatic act. 

Let me explain. This is what is known in moral theology as a “practical doubt.” About this “practical doubt” the Jesuit moralist, Father Slater, says the following. “If I eat meat with a practical doubt as to whether it is not forbidden on that day by the Church, I commit a sin of the same kind and malice as if I ate meat knowingly on a day of abstinence.” Apply this to the pontificate. If I refuse my subjection to the Roman Pontiff with a practical doubt as to whether or not he is the pope, I commit an act of schism. It’s a form of spiritual Russian Roulette.

[UPDATE: Sunday, April 15, 2018: 9:05 a.m.]

For those  who have succumbed to sedevacantism, I again refer you to Br. Andre Marie:

“Yes, and we all know what our Lord did. He deposed the high priest and declared the Seat of Moses vacant! Didn’t He?” The point is simply this: If the Man-God himself had enough respect for the sovereign pontiff of the law of types and figures as to say of the heretical Jew who was soon to murder Him, that he sat “in the seat of Moses,” how does anyone in the present law, the more perfect law, dare to do the opposite? 

Let me spell this out. Our Lord was not a sedevacantist. The evil deicide heretic who had authority over the “church” of Israel, was still the head of the true Religion. 
The religious society of the Old Law was still intact. Anyone wishing to save his soul could look to this office for leadership. Its sacrifices were accepted by God, and despite the abusive use to which it was put, the prophetical office was even maintained by this man. What did St. John say about Caiphas’ prophesy of our Lord’s death? “And this he spoke not of himself: but being the high priest of that year, he prophesied that Jesus should die for the nation.” No matter how you view it, the present Pope’s actions come nowhere near the iniquity of Caiphas.