The matter of sin was dealt with once and for all on the cross and God will never raise it again in judgment.
Believers will not appear at the judgment seat of Christ to answer for any sins that they committed before or after they were saved.
Christ answered for all those on the cross and God cannot call people to answer twice for something for which He already took His glorious Son to task, judged Him, punished Him, and made Him taste death for all men. The death of Christ will be meaningless if after He has died for all men, they should again be judged and condemned for the sins that He bore and died for.*
Believers will be judged (assessed) for what they have done with the things, opportunities, etc, that they were given to labour in establishing dominion.
Unbelievers will not go to hell because they have sinned. If that were so, believers would go to hell too; for believers, as unbelievers have sinned. Unbelievers will go to hell because they have refused to accept God’s answer to the problem of sin – the death of the Lord Jesus on the cross. Jesus said:
“Nevertheless I tell you the truth: it is to your advantage that I go away, for if I do not go away, the Counselor will not come to you; but if I go, I will send him to you. And when he comes, he will convince the world concerning sin and righteousness and judgment: concerning sin, because they do not believe in me; concerning righteousness, because I go to the Father, and you will see me no more; concerning judgment, because the ruler of this world is judged” (John 16:7-11).
Yes, concerning sin because they do not believe in Christ. Ultimately, sin is a refusal to believe in the Lord Jesus. All who do not believe in Him will be judged, not for their sins, but for not believing in Him.