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.
The Hindus note that you could end up getting bumped DOWN the ladder and end up as an insect. Buddhist beliefs are a tad more sophisticated, but they have the same idea of advancing through various Hells and Heavens until finally you achieve "release".
I think you want a hard and fast answer, and if so, check out any guru. He'll tell you what you want to hear.
Christian belief says that a "Man dies but once" ~ and there's a Resurrection (or maybe 2)". This creates the dilemma for a life devoted to sin, and then God's loving grace, and then sin again, and maybe back to God, then back to sin, and so forth. Just how do you deal with this if you have to wait for the Final Judgment?
The Scriptures suggest the "dead in Christ" simply wait, rising up every now and then asking "How much longer Lord". And that vision suggests that there may be many more "little short term resurrections" for all those dead folk rising up to ask questions.
Once you've pursued every possible avenue through all the major world religions to assist yourself in arriving at an answer to the question, I would suggest that no one knows (except Jesus).
So, there you have your answer ~ Be patient.
“The non-repentant evil person” was never truly saved in the first place then! Jesus is not going to lose his ‘sheep’ or his ‘gold coins’ (see Matthew 18:12-14 and Luke 15:1-10); He loves us all so much that He died for us. He also gave us free will—we can accept Him or deny Him. He doesn’t force us to do anything.