Are the sins of even the most wicked people already paid for?
Yes. The context states that Christ's death paid for all sin from Adam until the last person, including the vilest, lost, wicked people. Their sins are already atoned for and paid for; the only sin that brings eternal doom is rejecting the Gospel.
Les explains that Christ's crucifixion was not just another crucifixion; it was unique because He was the Creator God who took on human flesh so that God could pour out all His wrath for sin on Him. All sin from Adam to the last person who will ever live was laid on Christ and judged. Therefore, even the vilest member of a mafia or any lost, wicked person has their sins already atoned for and paid for. The only reason they would go to eternal doom is if they reject the Gospel, which is the one sin that puts a person out into eternal doom. The sin debt has been paid and finalized once and for all. Paul burned until his dying day to get the Gospel of salvation out to lost people.