May we reasonably hope that all are saved?
“No” says the Second Council of Constantinople: “If anyone says or holds that the punishment of the demons and of impious men is temporary, and that it will have an end at some time, that is to say, there will be a complete restoration of the demons or of impious men, let him be anathema.” [Denz 211]
To hope that a heretical claim is true is still a heresy. To say “perhaps” a heretical claim is true is still a heresy.
“No” says the Council of Trent: “Truly, even though He died for all, yet not all receive the benefit of His death, but only those to whom the merit of His passion is communicated.” [on Justification, Chapter 3]
The chief benefit of the death of Christ is eternal salvation. The Council of Trent infallibly taught that “not all” receive that benefit.
“No” says the Fourth Lateran Council: “He will come at the end of time to judge the living and the dead, to render to every person according to his works, both to the reprobate and to the elect. All of them will rise with their own bodies, which they now wear, so as to receive according to their deserts, whether these be good or bad; for the latter perpetual punishment with the devil, for the former eternal glory with Christ.”
The General Resurrection includes the reprobate in Hell, and these reprobate souls, having been given a resurrected body, will next be sent to “perpetual” (i.e. eternal) punishment with the devil.
“No” says the Council of Florence: “But the souls of those who depart this life in actual mortal sin, or in original sin alone, go down straightaway to hell to be punished, but with unequal pains.”
If no human persons are sent to Hell, then there can be no unequal pains.
“No” says the Council of Florence again: “Finally, unless they repent from their hearts, perform deeds worthy of repentance and make worthy satisfaction to your holiness and the universal church for the enormity of their sins, may they be thrust with the wicked into the everlasting darkness, doomed by the just judgment of God to eternal torments.”
If there are no wicked human persons in Hell, then the above infallible teaching would be false. The Council of Florence also taught, similarly to the Fourth Council of the Lateran, that the General Resurrection includes “those who have done evil” who will be sent “into eternal fire”.
“No” says the Fifth Lateran Council: the Lord “promises eternal rewards and eternal punishments to those who will be judged according to the merits of their life” [Sess. 8]
The promise of the Lord Jesus Christ of eternal punishment for those who die in final impenitence would be a false promise if no human persons are sent to Hell.
“No” says the First Vatican Council: “Since, then, without faith it is impossible to please God and reach the fellowship of his sons and daughters, it follows that no one can ever achieve justification without it [faith], neither can anyone attain eternal life unless he or she perseveres in it to the end.” [Dogmatic Constitution on the Catholic Faith, Chap 3].
If all attain eternal life, then this teaching of the First Vatican Council would be null and void; it would be meaningless and false.