"That was sold to Satan some time ago. Satan is now collecting the debt."
I don't think that makes it impossible for God to have mercy on his soul. It could happen, and I hope it does; I'm liable to need a little mercy myself, and if Saddam can get some, maybe I can, too.
Old Roman proverb: Ask not for justice; you too will be judged. Having him hang is all the justice we can really expect on this earth, and we really need to hope we don't get what we deserve when it's our turn to "shuffle this mortal coil."
Saddam Hussein, RIP. God have mercy on his soul.