If there is no God, morality is subjective. Mao, Stalin, Hitler, and every other murderer throughout history were doing what was right in their own eyes. Your question is too limited, even as a hypothetical. God is the model for perfection. Murder, theft, loving anything more than the God who created everything; is rebellion against God's standards. As unforgiven sinners that have broken God's laws we cannot join Him once our bodies die.
