Apparently, you don't understand what you are reading. Everybody knows what "ipso facto" means, and you just totally rephrased it to say what the Saint and Doctor did not say. "by the very fact" of his becoming an obvious heretic, he falls from his dignity and out of the Church. Then it says "and the Church must" - follow with some action upon that man who is "out of the Church". That action is performed on a man who is NOT pope, otherwise it would be the condemned heresy of Conciliarism (Gallicanism) to judge a pope. A pope cannot be deposed; other Catholic sources say this explicitly. Nor is the man a pope because he may still possess the Apostolic See. The See is not the man. Possession does not mean ownership.
Quote from: St. Francis de Sales:
"we do not say that the Pope cannot err in his private opinions, as did John XXII.; or be altogether a heretic, as perhaps Honorius was. Now
when he is explicitly a heretic, he falls
ipso facto from his dignity and out of the Church, and the Church must either deprive him, or, as some say, declare him deprived, of his Apostolic See, and must say as St. Peter did: Let another take his bishopric."
Heresy is a sin and a crime. St. Francis is talking about a Pope who has been convicted of heresy. He becomes "explicitly a heretic" when the Church has judged him a heretic. Again only the Church can declare a Pope a heretic and deprive him by deposing him.
Catholic theologians have said throughout the centuries that heresy is the only time an inferior can judge a superior. Cardinal Bellarmine, Cajetan, Suarez, and John of St. Thomas all taught an ecuмenical council can try a Pope for heresy and depose him. St. Francis De Sales lived in the times of Bellarmine and Suarez. He knew their positions and commented on them.