The other half was eaten by the Death God along with the 4th's soul....don't you guys pay attention.

That was the big question when the 3rd used the technique on Oro and said it was the same one used to seal the Kyuubi. If the technique sends the user and his target to the death god, how did the Kyuubi get sealed inside Naruto?

Now it's obvious the 4th sealed half inside Naruto and took the other half with him into death.