If Jesus wasn't crucified, Christians wouldn't be free from sin, so as a Christian if you had the chance to save Jesus, would you do it or let the Romans kill him?

Let me respond to the core of the question, “As a Christian, if you had the chance to save Jesus, would you do it or let the Romans kill him?”

If a Christian is someone who follows Jesus Christ, then a Christian, by definition, will let the Romans kill Jesus.

Jesus himself answered this question on the occasion when he first began to show his disciples that he should be killed. (Matthew 16:21-24)

Peter, on that occasion, contradicted Jesus, “This shall not happen to you.”

Jesus told Peter, “Get behind me (take the place of a follower), adversary. You savor not the things of God, but those of men.”

Then Jesus said, “If anyone will come after me, let him deny himself, and take up his cross, and follow me.”

The commandment of Jesus to deny oneself means to suppress those things of men which make one opposed to the killing of Jesus.

In short, Jesus said to his disciples, “If anyone will come after me, let him suppress his opposition to me being killed.”

That is the answer Jesus gave to the question, but I say it is, only in my own name.