>>42555270Lillie being erased means that Nebby escaped on its own and you/Hau rescued it on the bridge without her breathing down your neck.
Then a bunch of nothing happens. Gladion already fills the role as child of the villain who was treated like an object, so much in fact that he had already started to go through his developmental arc before the events of the game even begin- he starts to harbor ill-feelings towards Lusamine, becomes rebellious, starts to dress himself how he wants, steals an experimental Pokemon, etc. He does all of the things Lillie does but so much better in addition to actually helping the player or battling them. His role would have been given even more purpose without the existence of Lillie, if anything. Heck, even Hau would've had more purpose with her gone.
At the climax of the story in Ultra Space, Lillie's hissyfit and pathetic attempt at a character arc doesn't impact the events unfolding or the actions of any other character. It's so self-contained that it being wiped would not do a thing to the the story or Lusamine's following actions.
Lillie exists only as otaku/waifubait for people with basic taste. That's it.