Not wishing to start a theological flame war on Kate's LJ, but theories of the Atonement are diverse and contentious. There's a significant school of thought that sees the Incarnation of God as a human being, and the return of that human being to God after death, as bridging the gap between the two and making them "at one".

For that, any death would do -- and, since being mortal is a part of being human, Jesus' death in some form was inevitable. (I heard a very interesting talk which pointed out that, if he truly partook of the human condition of those around him, he stood a very substantial chance of being miscarried or dying in infancy.)

The way I see it, the lesson of the Crucifixion relates to human nature, not to God's.