And, it's entirely possible the person DID get born again, but as Jesus taught in Mark 4:13-20 they allowed persecution, affliction, cares of this world, lusts for other things or deceiptfullness of riches ENTER IN and choke God's Word out of their lives.
Jesus teaches us in John 15:1,2 that those that do not abide in Him and do not bare fruit are cut off. Romans 11:22 is a similar warning.
Bottom line is the Christian should recognize being a believer is like a marriage relationship between us and the Lord.
If you turn away from your wife and go committed adultery, she has every right to divorce you. Of course the Lord gives us opportunity to repent and come back to Him, but we also run the very real risk of being turned over to a reprobate mind as we see in Romans 1:28-32
But, based on numerous warnings in the NT... if they continue being carnal without repenting and going back to walking after the Spirit... they would not be going to Heaven.
The Lord says thru Paul...
Romans 8:6 - For to be carnally minded is death; but to be spiritually minded is life and peace.
”Death” in this context is being separated from the Lord just like the Lord told Adam and Eve in the garden that if they eat of that tree they shall die. They lived physically for 900+ years so we know the Lord is not referring to dying a physical death...
We see in Galatians 6:7,8 that is we sow to the flesh (sin, aka not being led by the Spirit) we shall reap corruption which again is is being separated from the Lord
Romans 8:13, 14 - For if ye live after the flesh, ye shall die: but if ye through the Spirit do mortify the deeds of the body, ye shall live.
For as many as are led by the Spirit of God, they are the sons of God.
This is why the Lord says in 1 John 1:9 that if we confess our sins He is faithful and just to forgive us and to cleanse us.
He would not need to say this if we were not capable of turning away from the Lord and disqualifying ourselves where our salvation could never be lost. We also see the Lord saying that we must forsake our sin on order to have mercy:
Proverbs 28:13 - He that covereth his sins shall not prosper: but whoso confesseth and forsaketh them shall have mercy.