I suspect that justice is inevitable, with or without a God.
The impossibility is in the reliability of calling it up during the life time of a victim.
You're unjust, you'll pay; but you're not likely to pay your prey.
If I harm you, the state may sue me on your behalf. The state then pockets the fine for itself. I hope God doesn't intend to do that.
I hope for a next life so that fines can catch up to victims. Man, I'll be on easy street.