The New Testament teaches that there is some kind of judgment, some kind of accounting, for all of us after death. We all will stand before the throne of judgment. Whether this judgment and accounting happens at one's immediate death or at the final judgment (the "general resurrection"), all of us will give an accounting for the lives we have lived "in the body" (Matt. 12:36; 1 Cor. 3:15; 2 Cor. 5:10). Can you imagine standing before God and accounting for your own actions throughout your life? How did we treat the poor and the "little ones" among us (Matt. 25)? Now, imagine going into judgment with a litany of crimes against humanity and God behind you. The offer of forgiveness in Christ does not exclude justice or judgment after death. But the intent of justice and judgment is restorative and regenerative, not retributive and vindictive. The objective of the atonement is restorative justice and the establishment of peace—what the Old Testament calls shalom: victory over death, liberation of the oppressed and oppressor, and peace between God and fellow human beings.
In a more holistic vision, it makes sense to consider—as some theologians have—whether this life represents our "final answer," or whether might there be further opportunities (e.g. "post-mortem") to repent. There are plenty of biblical warnings about making the most of our chances in this life. But we do not have a clear and compete knowledge of the life to come. The possibility of repentance after death, even for the vilest of sinners, focuses our attention on the biblical picture of God's intent for universal justice, for the reconciliation of sinners and all creation. The restoration of shalom will require that the oppressor and the oppressed, the perpetrator and the victims, be reconciled. What makes that restoration possible is the cross of Christ.
The conversion of Paul reminds us that, in the economy of God, even the worst of sinners can be saved. This forces a question upon us: If we were to meet Osama bin Laden in Heaven, could we accept him? Do we believe that the blood of Jesus can cover the most violent sinner, even if that sinner turns to God in the very last moment of his life? And if God could forgive such a sinner, could we?
We should be reluctant, to the point of refusal, when asked to surmise the eternal destiny of any human being. We just don't know. Our honest ignorance of such matters should shape the way in which we relate to our enemies here and now. We rightfully anticipate divine accountability and justice. But if God were to give mercy and forgiveness to our enemies, could we do the same?