If God is omnipotent, and all wise, why can't he come up with a way to save people who changed their minds after they died?
Because we don't have a thinking mind after we die earthly death. We don't have a functioning mind in the grave.
Ecclesiastes 9:5-6
For the living know that they will die,
but the dead know nothing, and they have no more reward, for the memory of them is forgotten. Their love and their hate and their envy have already perished, and forever they have no more share in all that is done under the sun.
Psalm 115:17
The dead do not praise the Lord,
nor do any who go down into silence.
All who die earthly death are in a dormant state until either the 1st or 2nd resurrection.
1st Thessalonians 4
The Return of the Lord
13Brothers, we do not want you to be uninformed about those
who sleep in death, so that you will not grieve like the rest, who are without hope.
14For since we believe that Jesus died and rose again, we also believe that God will bring with Jesus those who have fallen asleep in Him.
15By the word of the Lord, we declare to you that we who are alive and remain until the coming of the Lord will by no means precede those who have fallen asleep.
16For the Lord Himself will descend from heaven with a loud command, with the voice of an archangel, and with the trumpet of God, and the dead in Christ will be the first to rise (1st resurrection).
17After that, we who are alive and remain will be caught up together with them in the clouds to meet the Lord in the air. And so we will always be with the Lord.
18Therefore encourage one another with these words.
1st Corinthians 15
51Listen, I tell you a mystery:
We will not all sleep, but we will all be changed—
52in an instant, in the twinkling of an eye,
at the last trumpet. For the trumpet will sound, the dead will be raised imperishable, and we will be changed (1st resurrection).
53For the perishable must be clothed with the imperishable, and the mortal with immortality (eternal life).
Humans are mortal ... we do not receive immortality until Jesus returns, until then all are in the grave described as a sleep .... because final judgement has not yet occurred.
The 2nd resurrection (of the lost) will be resurrected later and will not receive immortality (eternal life)
Do not marvel at this; for the hour is coming in which all who are in the graves will hear His voice and come forth—those who have done good, to the resurrection of life, and those who have done evil, to the resurrection of condemnation.
John 5:28-29 NKJV