Without Green, who would your starting RB be?? Davenport can't stay healthy in a backup role, so it's unlikely he could handle the beating of being the starter. Fisher is a solid 3rd down back, but hasn't shown he can be a threat as the main guy. Williams had a chance to prove himself last year when Green and Davenport went down, but he got injured early in the game.
there is some logic to trading one of them because there's a good chance the Packers will lose both, if not all 3 rbs next year (I believe fischer only signed a 1 yr. deal), and then get NOTHING in return.
Granted, I'm not really offering solutions because I'm not too fond of losing any of those guys during the season...so I suppose I'm just playing devil's advocate.