A one time event does turn perfect people into those God consumes with fire. That is different than being a sinner and constantly in need of salvation. There was no salvation for those consumed with fire. Do you think Adam repented of his sin? Do you have a verse that proves your point?
This is what Paul claims: Romans 5:12-14
"Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:
(For until the law sin was in the world: but sin is not imputed when there is no law. Nevertheless death reigned from Adam to Moses, even over them that had not sinned after the similitude of Adam's transgression, who is the figure of him that was to come.)"
What Adam's descendants known as sinners were, was different from Adam's disobedience, transgression of a specific Law.
When sin is eradicated, there is still the law defined in ruling with Christ. The Millennium is not without laws. What it is without is the sin nature and sin caused by Adam's disobedience. Will it be called sin when a law is broken? Not like we understand sin. Yes, if a Nation does not obey the law, there will be consequences. But not like Adam's disobedience, that brought sin into the world. There will still be a death penalty for disobedience. It will be like it was for Adam and Eve, before they disobeyed the one law God gave Adam. They died the minute Adam disobeyed. God let them live in dead corruptible bodies. In the Millennium disobedience will be immediate removal from life to Death. No prison, no rehab. To die will be considered a curse. A nation, like in Zechariah, will pay as a whole group if they refuse to follow the law. The point is no one will be compelled to break the law. There will be no reward. Today in sin, we are rewarded for bad behavior, at least that is the short term success of being a sinner in current sin conditions.
You explain what sin eradicated means then. Are nations punished for not bringing a sacrifice to Jerusalem since the Cross? Will there be sin in the NHNE where Nations do not bring an offering to Jerusalem?