You make a fantastic non-sequitor, this constant appeal to the logic that if someone can come to Jesus without being preached to than Jesus died in vain.
Is Abraham in Hell? David? Moses? Isaiah? Elijah?
Here's one: Point to me a single bible verse where Jesus preached that we should release prisoners. Can you? True, the New Testament hardly recalls EVERYTHING that Jesus did, but it's sort of a glaring omission, since right at the start of his ministry, Jesus states he came "to bring glad tidings to the lowly, heal the broken-hearted, to prolcaim liberty to the captives and release to the prisoners." Yet Jesus teaches to be visit prisoners; he doesn't release them.
So what does this passage refer to?
St. Peter explains (1 Peter 3:18-120): "For Christ suffered for sins once, the righteous for the unrighteous, that he might bring you to God, put to death in the flesh, but quickened by the Spirit. IN IT, HE WENT TO PREACH TO THE SPIRITS IN PRISON." In other words, be being put to death, he came to life anew, and in that newness of life, he preached life to those spirits in prison. But here's the proof that St. Peter clarified that he doesn't mean living souls in an earthly prison, but, rather, the souls in hell: "IN IT HE WENT TO PREACH TO THE SPIRITS IN PRISON, WHO HAD BEEN DISOBEDIENT SINCE THE LONGSUFFERING GOD WAITED IN THE DAYS OF NOAH, while the Ark was being prepared, wherein few, that is, eight souls, were saved by water."
So Christ preached to the souls in Hades. They had not known him in life, so he came to them even in death to win their salvation.
Of course, they died BEFORE Christ's crucifixion. What difference distinguishes them morally from those who died before word of Christ reached them? None.
"... I will build my Church, AND THE GATES OF HELL SHALL NOT WITHSTAND AGAINST IT."
In other words, "my Church will destroy the very gates of Hell!" Then why worry about saving souls now, if they can still be saved after death? Because we can call souls to repentence, strengthen waivering souls, and heal the pains and sorrows which lead to despair!
Revelations 20 gives more detail. It describes a future scene of how AFTER the Resurrection of the holy souls, "... the sea gave up its dead; then Death and Hades gave up their dead. All were judged according to their deeds. The Death and Hades were thrown into the pool of fire (This is the second death.) Anyone whose name was not found written in the book of life was thrown into the pool of fire."