I don't think anyone including Naruto would be able to release the Kyuubi without the key. With the way things have been going lately with Akatsuki and all, I think that if and when Naruto finally receives the key he will have to use it to release the Kyuubi.

Whether that would be freeing the Kyuubi, being able to temporarily release the Kyuubi like Gaara was able to do to Shukaku or simply just being able to go nine tails remains to be seen.

Since the seal requires a key to be opened then I think that if Naruto does indeed die if that doesn't immediately kill or release the Kyuubi I think it would simply remain inside his body. If the seal can't be removed without a key then that could explain why Akatsuki hasn't taken any overly aggressive actions against Naruto yet.