How come this person died?

Question

Spoilers ahead

In The Legend if Korra, in season two, when Vaatu and Unalaq fuse they make a 'dark avatar.' How come when Korra destroyed Vaatu instead of Unalaq he dies instead of retuning to his body?

Answer 1

If you watch the scenes where Unalaq becomes the Dark Avatar, then defeats Raava...you see that Unalaq physically transformed into the huge being that went to attack Republic City. Unlike Korra, he was not Astrally Projecting, that was actually his body that had been transformed into an immense spirit by his fusion with Vaatu.

In essence, unlike the symbiotic, parallel existence that the Avatar had with Raava...Vaatu merged completely with Unalaq to create a new spiritual being. So when Korra destroyed Vaatu with her Spirit Bending, that was Unalaq's Body she destroyed.

Furthermore, Unalaq mentioned in Book 2, Episode 10 that Spiritbending could be used to obliterate a human soul. Normally, people are apparently protected from this because their soul is safely housed within their physical form (we never see Unalaq use this ability on someone who is not Astrally Projecting), but due to his merger with Vaatu, Unalaq cast aside his physical body in favor of turning into the enormous super-powerful Unalaq/Vaatu hybrid. So the Spiritbending method that Korra used to purify and dissipate Vaatu's soul also dissipated Unalaq's soul.

So, in short...he didn't "return to his body" because he had been irrevocably transformed into something else by Vaatu (unlike Korra who was that big because she had left her body behind and turbo-charged her soul via the Tree of Time). And thus, when Korra destroyed the giant form with Spiritbending, it destroyed Unalaq's body.