Then that person was never truly saved in the first place. Like he said, once saved, ALWAYS saved (unless you commit the unpardonable sin-denying the Holy Spirit).
If we regret and try to repent and to attempt to avoid sin, then that is reasonable. We have a sin nature and are weak.
If you have sin parades, do not repent of your sin and go on with the sin like it is normal, I think you may have something to deal with on judgment day.
It is possible to accept Christ in the past, corrupt yourself with temptation and to become evil.
Does the non repentant evil person get the benefit of a previous salvation they didn’t take advantage of or honor?
I can’t see how they could.