Common sense says that once a person is born, they cannot be unborn. In the gospel of Christ, once a person is born again, they cannot be un-born again. The promise of Jesus Christ is eternal life to those who are born again and they can never perish.
27 My sheep hear my voice, and I know them, and they follow me: 28 and I give unto them eternal life; and they shall never perish, neither shall any man pluck them out of my hand. St. John 10.
When preachers tell people that even after they are born again of water and of the Spirit that they can still go to hell this is a lie. If a person goes to hell after serving the Lord, then they were never born again. When the people came to Jesus saying "Lord, Lord, open unto us" (St. Matthew…) and Jesus said that He knew them not, those people were not His children. They were not born again and never had been.
God has given no man authority to tell another soul they are going to hell. Jesus only, is the giver and taker of life; He has the keys of life and death and no man can ever determine the destiny of another being's soul. If a preacher knows not for sure whether a person will actually descend into hell after their death, then they should never say they will. The only reason preacher's use this theory is for scare tactics, to bring people into subservience.
It is by faith that any person will go to heaven. If a person believes they will ascend to God at His coming or after their death, it is by their faith they will. If a person believes they can go to hell even after they are born again, they will live under fear the rest of their lives. Believe in salvation and trust in God's words, not man's words.