"Promise me one thing- just one thing only."
Frisk nodded vigorously.
"No one can know about this whole reset thing. Not Papyrus, not Asgore, not anyone. It would basically bring this world to the point of falling to pieces at our feet. If we weren't trapped between time and space already, very few of us wouldn't be able to handle that knowledge, and could drive those who couldn't to the edge. So, please. I'm begging you. When you reach the End, when you get us out of here for the umpteenth time, I don't care if you reset or not. Just don't tell anyone about it, and... Please don't go homicidal again, okay?"
Frisk smiled meekly, and nodded. "I can do that. And don't worry about the reset."
They gave Sans a small hug. "After that whole thing with Chara, there won't be any more."
And with the final word, they opened the door to leave; before exiting they paused. "See you later."