Based on the final scene from "Enchanted", we see the impact that Dipper and Mabel left in Gravity Falls, when they left. (Song: 10538 Oveture from "American Hustle".)
Mabel treats Dipper just as cold as Robbie treated him (i.e. Mabel saying that Dipper is his real name, and not Tyrone, accusing Dipper of her mistakes, when it was her fault)