Trezeguet can just score, but he can't create game like Zlatan can, so IMO Trezeguet is not so good as Zlatan is. So I think, that after that season we should definately sell him ( as far as I know he's got big wage).
About Mutu. We don't know what impression drugs and that scene about Chelsea left on him. So if there would be the old Parma's Mutu, he would be definately be tter than Trezeguet is, but if ther would be Chelsea's Mutu, I would think twice.