What does Natalie discover in Act 2, Scene 14? What song is sung?

Natalie arrives home, finding Dan sitting alone in the dark and learning that Diana has left. In the final song of the show, she sings that what they need is light, and that they'll keep on living ("Light"). Dan comments that they've been waiting too long for things to be made right. Diana appears in another place, singing of the need to move on and finding a way to survive.