At the end of chapter 2, Toriel suspecting that someone was wandering around the house at night decides to call the police. The most accepted theory is that in chapter 3 Undyne and Toriel will end up in the Dark World and if there is a wierd route, we will possibly end up making Toriel burn Undyne.
However, I think that this will not be the case, but that Napstablock will come in Undyne's place because he is an officer like her, or a third option, if we talk about the Dark World to Undyne, she laughs so much that she ends up releasing the trapped charroros, so she will be busy and the night will be Napstablock, but if you don't tell her, she will come