Details: The next day, you and your mother awakes to a ring at the door. She, of course, believes Kukui ill barge right in. Instead, as the two of you go to answer it, Hau comes charging in. He's in a frantic state, saying you need to come with him immediately, that Lillie is leaving.
The two of you quickly arrive at the Marina of Hau'oli City, where you first see Kukui explain to Lillie that it was too hard for his wife to come say goodbye, but both of them still wish her luck and that there doors are always open to her.
As Hau and you make it, Lillie does confirm that she is indeed leaving, for the Kanto Region, where you hail from, no less. She tries to explain that she's doing it for both her and her mother, wanting to become a real Pokemon Trainer for both of them, having been inspired from you. (Another reason, a more truthful one, will later be told to you from Wicke why Lille picked Kanto specifically.) Hau takes it hard, but all of you understand her decision. She also thanks both Hau and yourself for being friends to her, thanking you specifically for having been able to travel with you.
After she leaves and waves as she does, Kukui tells both of you that sometimes its hard to say goodbye, but a smile is all it takes to show support for someone you love. He then suggests the three of you return home, instead of bumming around, to the people that love you.
The credits then roll with many pictures of the people you were able to meet along the way and the adventures of such, ending with a picture of a package on a desk. Then some writing comes on the screen, a letter from Lille to you. She repeats another quote about what a smile means, before saying just how glad she was to have had the pleasure of meet you.
The main storyline is now over, but the game is far from completed.