If a person commits an offense against the written Torah laws that requires death as the penalty, but is not put to death because modern laws are different, is that person required to kill themselves to fulfill the penalty? If they do not kill themselves then how do they atone for the offense?
Definitely not! Although the death penalty is mentioned in the Torah for severe crimes, the Talmud tells us that the threat was almost never carried out even in the “olden days”, but mainly serves as a deterrent and way to stress the severity of those actions. As we say in the prayer on Yom Kippur (U’n’taneh tokef), “For God doesn’t want the sinner to die (!), but rather that he should return and improve his ways and live. Until one’s very last day, God anxiously waits for him (to change), and if he repents, he will be accepted immediately!” In short, the simple and only way to atone is to apologize, and act differently.