<3 this design, and nothing against the return to humor (especially given today), but for some reason it felt a bit more serious to me.
If I may, this is what my brain came up with:
"You don't know what's out there." She reached out to take his hand, hoping, perhaps, that her touch alone would stop him from leaving.
"No one does, but that's why it's worth exploring. Don't you see? There could be a world out there beyond the water, a world that allows us to do more than just live in the darkness and scramble through up our ladders." He responded, taking a step forward, turning away from her - but not letting go.
"But the elders said that this is where we belong-" she protested weakly, though she too wanted to explore the world beyond, the world outside of their ramshackle dwellings and scrap houses built from the pieces that came down the waterfall into their cave.
"That's because they're afraid, because no one ever comes back. But just because you can't come back doesn't mean you shouldn't go. I want to find out what's out there, and bring that knowledge back. I want to make it so that we have room to run and play, change it so that we're not always living in the dampness, in the darkness, forever."
She realized that she could never keep him, that he was set on exploring the world beyond, no matter how dangerous it was. He wasn't satisfied with staying here and being with the others; he had questions, and would never settle for anything less than knowing the answers.
And all she could do is squeeze his hand. "I'll come back," he said, fondly, that same old lopsided smile on his face, though it was more than a little sad, now.
"No," she answered, taking a step forward and looking out the wall of water. "We'll come back."