I think we have to go back to the context of your using Grayling's employment of the Polanski case in the defense of hell. There are some important differences between this kind of criminal case and the problem of sin. Grayling would not have been making his case if Polanski had served his full sentence and was about to be released. The point is that our judicial system allows people to be released from their punishment once proportionality is reached (with a lot of other considerations thrown in as well). The passage of time without punishment doesn't release one from guilt, that was Grayling's point. In our judicial system, the doing of time in prison "pays one's debt to society."
You are the one using the criminal reasoning to justify hell. But the analogy to the criminal justice system is precisely what propels the proporitionality objection. To get a defense of hell of the ground you have to argue either that the case is different with sin because it is against God, or argue that the damned sinner is unrepentant and therefore reoffends continuously. Those are precisely points at which the criminal justice analogy breaks down.
In my view the retribution analogyis too closely connected to the concepts of criminal justice to justify hell, and that is why I think of hell primarily as a natural consequence of the fact that one is rebelling against the source of goodness itself. If you're doing that, you can't be happy, and here case of Aslan and the dwarfs and the Great Divorce helps us see that. No fire and brimstone is necessary to make us miserable if we are trying forever to find happiness apart from the Source of happiness.