Does Amara Kill God?

God's dying, which leaves Amara free to end all of creation because the cosmic balance between light and dark has been destroyed.

Who kills Amara?

Episode 17's fallen character is Amara/The Darkness, and the chances of her pulling off a similar comeback rest solely on the fate of her brother, Chuck/God, who just so happens to also be the one responsible for her demise. An action that has now made him immeasurably more powerful than ever.

What happened to God and Amara?

Amara was left severely damaged by the attack, but upon confronting God, she could not accept being locked away again, and attacked both God and Lucifer, leaving one to slowly die and the other seemingly dead, but no longer in his vessel, Castiel.