Ezekiel 18:20 The soul who sins is the one who will die. The son will not share the guilt of the father, nor will the father share the guilt of the son. The righteousness of the righteous man will be credited to him, and the wickedness of the wicked will be charged against him.

 

Romans 6:23 For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord.

 

1 Corinthians 6:9-10  Do you not know that the wicked will not inherit the kingdom of God? Do not be deceived: Neither the sexually immoral nor idolaters nor adulterers nor male prostitutes nor homosexual offenders 10 nor thieves nor the greedy nor drunkards nor slanderers nor swindlers will inherit the kingdom of God.

The answer is eternal death and not being able to enter or inherit God’s Kingdom.  The fate of or penalty for an “unsaved” sinner is a Godless eternity.