Avatar Connection

The Avatar Connection also known as The avatar cycle. If a Avatar dies below the age of 16 or dies in the avatar state will end the cycle. So if Aang dies the avatar state will end.

Raava is linked to only one soul, Wan's soul, wich is Aang's and Korra's soul. It's probably because she (Raava) has control over the Avatar (or at least her spirit is active) and if you kill the Avatar in the Avatar State, than not only the Avatar dies, but also Raava.

On the other hand, it definitely seems probable that dying in the Avatar state could destroy all the Avatar's previous lives, which pretty much amounts to the same thing given how it effected Korra.

What happens to Raava when the Avatar dies?

Because when the avatar dies it’s like the human body dies and the spirit of a Raava moves on, but if they die in the Avatar state, Raava herself pretty much dies too. What do you think?

One thing that has been bouncing around in my mind since 'Beginnings Part 2' is how the great Avatar Wan died. At the end of Beginnings part 2 the scene cuts to a worn down and wounded Wan, in what appears to be a battlefield. The Landscape itself looks like a war zone.

Because a human spirit cannot be reborn or made immortal, the Avatar cycle simply bonds her to another human soul, then through the spirit of Raava, that human is connected to all the past Avatars. So when an Avatar dies, the human side goes to the spirit plane, while Raava is passed on.