When Jesus was on the cross, one of the men being crucified next to Him came to his senses and said, "Lord, remember me when You come into Your kingdom" (Luke 23:42).
So Jesus said, "Assuredly, I say to you, today you will be with Me in Paradise" (verse 43). You might describe what happened to this man as a deathbed conversion. And this gives a measure of hope to those who maybe have given up on certain people who have no need for God—or at least think they have no need for God. Don't stop praying for them. Because I have heard glorious stories of people coming to Christ right before their deaths. My own mother did not really come to Christ until about a month before she went to Heaven, and I had prayed for her throughout my life as a Christian. Maybe you feel right now that someone you know never will come around. But they may.
Or sometimes we fear that certain people who have died are in Hell right now. But we are not in a position to say who is in Hell. I do think I can authoritatively say who is in Heaven, because if a person has put his or her faith in Christ, the Bible assures us that this person is in Heaven. But unless you were with someone when they passed into eternity, you don't know what happened. It is possible that someone you shared the gospel with, someone you told about Jesus, perhaps put their faith in Christ in the last few moments of their life. And you might be surprised to see them in glory some day.
I think there will be some surprises when we get to Heaven. So don't give up on the people you are praying for.