Depends on where... Obviously in the middle of a crowded area where people gather no one is just going to leave a corpse to rot. In this case it should just vanish after a little while (someone is bound to clean it up)
If your in a cave or a place where no one is gonna really poke around then yea the body should decompose.
Of course in the grand scheme of things that's just one of those neat little things that doesn't add enough to the game to be worth the time it would no doubt take to implement, when your developing a game you have to be careful with your resources and stick to primary priorities over little admittedly meaningless details that would just make someone go "cool" then never get cared about again.
True, but these tiny little details people don't pay attention to really do make a difference. Although you may not notice it, it makes a huge difference in your gameplay experience.
For example, you could play a game at 30 fps, which is perfect for a fluid visual experience, or you can have a game at 60 fps, you won't notice it, but you will 'feel' a smoother, better experience when playing, something just makes this game a little more enjoyable.
Its the little things that make the difference between a good game, and a great, innovative game.