The New Testament teaches that we must continue in faith until the end.
However that being said, the parable is not about born again Christians and backsliding. It is a parable to teach the Pharisees that their attitude about being upset that sinners where eating with Jesus was wrong. He is saying they are like the elder brother in this parable and they should be glad that sinners who need to repent were interested in what Jesus was teaching.
But as to Christians that backslide and start drinking and fornicating and bar hopping. If they keep living that way they will go to hell.
However that being said, the parable is not about born again Christians and backsliding. It is a parable to teach the Pharisees that their attitude about being upset that sinners where eating with Jesus was wrong. He is saying they are like the elder brother in this parable and they should be glad that sinners who need to repent were interested in what Jesus was teaching.
But as to Christians that backslide and start drinking and fornicating and bar hopping. If they keep living that way they will go to hell.