In canto 20 of Dante's Paradiso, Dante describes what Ciardi's footnotes on lines 106-117 say is a pious tradition that Pope Gregory (540-604) prayed for the salvation of the Emperor Trajan (53-117) and he was revived, preached to (by Jesus Himself), converted and went to Heaven.
Dante follows a legend that Gregory I prayed so ardently for the salvation of Trajan that God's voice replied "I grant pardon to Trajan" Since God so granted, it was, of course, predestined that he should so grant. Trajan therefore, could never have been truly damned, for no prayer can help the damned. But since none may go from Hell to Heaven ( with the exception of those souls Christ took with him in the Harrowing of Hell), it was necessary to restore Trajan to the flesh long enough to permit his conversion to Christ
This would appear on the level to be against what Our Lord said in the parable of Lazarus and the rich guy, that "None Shall Pass" from one side to the other. However, it also seems to be skirting around the very real and miraculous notion of revivification (i.e. where was the other Lazarus's soul when he died; did he receive particular judgement?).
So, maybe it stands to reason that our more virtuous ancestors may yet ascend to Heaven before the last day? In any event, is that the mode of ascent promised at the end of time?
if it happens at the end of time, is a second (or third) death required?
Note, I tried putting a bounty on this question so I could get an answer to my question, but didn't get what I was looking for.