Nice Fire Emblem reference, but Raava already said she can't "kill" Vaatu because they must live together in the world. the best that can happen is a world of peace or chaos for 10,000 years until they come back. At least that's how I interpreted it.
In case you didn't know, I have a comic book called Guardians. I'm the writer/creator of it, and we have four issues out right now, with our fifth coming out soon!
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