I mean, you sorta said it in the post: Now matter how many lives the personification of evil infects and destroys, it's always punished to some degree. Often to a great degree. Even if just by happenstance, like Chigurh getting creamed by a car running a red light. So even if Malvo is the Apex Predator or the Snake in the Garden of Eden himself, the idea that he'll just get away none the worse for wear would go against the Coen Brothers entire body of work.