Complex sentence: As Korra fights this figure, her link to the previous Avatars is broken; but with the help of Tenzin's daughter Jinora, she defeats Vaatu and Unalaq, and leaves the spirit portals open, allowing a new coexistence of spirits and humans.
Split into simpler sentences: As Korra fights him, her link to the previous Avatars is broken, but with the help of Tenzin's daughter, Jinora, she manages to defeat Vaatu and Unalaq. She chooses to keep the spirit portals open, allowing a new coexistence of spirits and humans.