The idea that by dying sinners pay for all their sins in life fits Watchtower wishful thinking theology.
But Romans 6:7 is talking specifically about anointed Christians. We, who are dead in Christ are to live after the Spirit. Just as those who die physically are free from further sinning, so should the Christian, being dead, live free of sin.
Unlike the anointed who have received the gift of justification, the majority of mankind are on another wider path that leads not to life, but to destruction. Jesus did not give sinners a false warning. He did not say, you don't have to repent as long as you die you will end up in paradise. Rather he said “If you do not repent you too will die in your sins!” Sinners will be resurrected to condemnation and judgment; they will have to give an account for everything done in secret. Some will face more severe consequences for their actions than others. But ultimately the destiny of the wicked on the broad path is eternal destruction.