I don't think Jesus had to die. It was the obvious outcome of him living, but not what needed to happen. Just don't tell my congregation I think this, or I may have to go into another line of work. Now let me flesh out what I just said.
I have struggled with the concept of Jesus dying for my sins for years. Finally, I have just given up on it making any sense. There are several theories and interpretations of what happened, but none of them really click with me.
There is the ransom idea. Jesus paid a debt to the devil for me. So I belong to the devil and not God, and Jesus paid him off. Not wait, I belong to God, but the devil stole me, and Jesus paid to get me back. I'm getting passed around a lot without my knowledge. I suppose this is fine for a metaphor, but I could never buy it as actual. Why does God need to buy me back with dying anyway. Just kick that devil's butt without making me feel guilty.
Anselm interprets the cross differently than Origen. He says that sin is dishonoring God and we owe God honor. In order to fix the problem we either need to be punished or satisfy God. We deserved to be punished forever because we are just so awful, but God is merciful and decides to satisfy God's own honor by having God's son die instead of us. Perhaps this made sense as an explanation in the time of Anselm, but I think it makes God sound a little crazy. "You have dishonored me and must die, but that would not be merciful. I will kill my son instead to satisfy myself. " Can't God just get over it and move on? And would God really feel satisfied by killing God's son? God, you're freaking me out a little.
Then we move to the moral theory of Abelard which I barely understand. If I understand it correctly, Jesus shows us how much God loves us by dying on the Cross, and then we feel bad for what we have done wrong and repent. This one I can buy into a little more. Jesus was showing us a better way to live and was rejected and killed him. I can even relate this to how I respond to others. I reject that which is life giving more than I should. I feel bad about and try to repent. But where this breaks down for me is the I killed Jesus idea. No I didn't; I wasn't even there. Would I have killed Jesus? Oh, I'm sure I would have been in the crowd shouting for his death. It's an ok metaphor, but not based in reality. My life style helps kill people or at least doesn't do much to save them. I feel bad for them, but not Jesus. I try to change my life to hurt less people. I find Jesus my guide in this not my victim. (This theory makes some pretty cheesy camp skits.)
Then we have your friend and mine Calvin. Calvin talked about God being a just judge. We have sinned and need punishment. Someone has to pay the price for what we did! Really? Why is that again? Doesn't someone pay the price for what I do without Jesus dying? This is just ladling on the guilt. Now I'm depressed.
So, did Jesus have to die? Well, yes and no. Jesus didn't have to die in order to save me, but Jesus had to die because of the way he lived. You can't go against the established system as much as he did and expect to live. What saves me is the hope God gives us through Christ. There is hope is the Kingdom Christ proclaimed and ushered in. There is hope in the Resurrection that sin and death do not get the last word.
This post is getting way too long, so I'm going to stop. I'll end by saying that the event of the Cross is still very important to me personally and theologically even if it doesn't sound like it.