In the Latin original of Etsi multa we have a single sentence concerning the indefectibility and the new hierarchy:
Quote from: Pius IX, Etsi multa luctuosa
Eapropter denegant etiam indefectibilitatem Ecclesiae, blasphemantes ipsam in toto periisse mundo, proindeque visibile eius Caput et Episcopos defecisse : ex quo sibi ferunt necessitatem impositam legitimi episcopatus instaurandi in suo pseudo-episcopo [...]
Quote from: Pius IX, Etsi multa luctuosa
For that reason, they additionaly deny the indefectibility of the Church, blaspheming that the same would have perished throughout the world, and accordingly its visible Head and the bishops would have erred : wherefore they assert a self imposed necessity to restore the legitimate episcopate in their pseudo-Bishop
etiam here means additionally, since the word deny occurs for the first time. Before, the Old Catholics reject, oppose, boldly affirm, etc. But that's not all, they also deny the indefectibility. In what way do they deny the indefectibility? They do it by saying that the Church has perished, Pope and bishops have erred, and the legitimate episcopate has to be restored.
(They don't do it by saying that the Church has perished, Pope and bishops have erred, and the consummation of the age has begun.)
Pius IX concedes that there will may be a defection at the end of the age in the following way:
Pius IX compares the Old Catholics to the Donatists and adopts the reasoning of St Augustine. Augustine interprets the Psalm Call me not away in the midst of my days and tells the Donatists that they can't state that the Church has apostatized, since the consummation of the age has not yet come. How could the Donatists know that (at that time) the consummation of the age had not yet come? Augustine says: Non vides adhuc esse gentes in quibus nondum est praedicatum Evangelium? (Do you see not that there are still nations among whom the Gospel has not been preached?) This refers to Mt 24,14:
Augustine's reasoning is: An apostasy is not expected before the consummation of the age (i.e. in the midst of her days). Augustine therefore implicitly concedes, that an apostasy may happen at the consummation of the age.
P.S.: St Augustine elsewhere reckons with an apostasy at the consummation of the age. He comments on 2 Thess 2:
P.P.S.: With respect to my translation above: The word eapropter occurs in the encyclical Quanta cura of the same Pope Pius IX. vatican.va has an Italian translation where eapropter is translated as conseguentemente that's consequently. The English translation on papalencyclicals.net has for this reason.
The expression ex quo is used twice in Quanta cura. Translations are whereof or from which.
vatican.va: Quanta cura, Latin
vatican.va: Quanta cura, Italian
papalencyclicals.net: Quanta cura, English
I find your argument interesting and enjoy the presentation of the Latin, particularly the discussion of St. Augustine.
Having said that, note the pope says, "
[f]or that reason, they additionally deny the indefectibility." What reason? The one he just stated: they say the pope and the bishops in union with him in an ecuмenical council declared heresy.
Anyway, as I said, we largely agree on what V2 and what the conciliar church means - the gospel has been preached throughout the world, the apostate heretics have taken over and its the "discessio" (schism) predicted (2 TH 2:3) and it's the consummation of the age. We await the Lord's return, which is imminent.