Going grey is still something he'd appreciate though. Satan's main issue is the guilt he feels; he has been feeling and living it for like 5 billion years. So if he goes grey, even if just for a couple of month, it finally gives him some time to rest (even if short). Permanently die until the thing in Asgard is over, too. Killing him and resurrecting him until the point Satan would lose his memories and not being able to function is ALSO welcomed. As long he doesn't have to remember Akira, it's fine.

So all these options ARE the best. Locking him up would be the one that would torture him the most, technically.