I didnt expect to find a place for lost fics here but there we are!
I read a really long time ago, back on ff.net; a labyrinth fic in which Jareth used to take the role of the villain in order to make kids learn to be good, and to value and protect their younger siblings. There was at one point a flashback about another girl who didn’t learn the lesson enough and whose younger brother drowned and jareth made her think it was his fault so that she wouldn’t break under the guilt. It was really a case of jareth deliberately becoming the antagonist to force them to have a change of heart and prevent tragedies, no matter how much he would suffer and be vilified for it.
In that story the labyrinth reshaped itself for each new runner but this time jareth tried to preserve it, locking each part of it in crystals that he sent to sarah so that they wouldn’t be destroyed in the reset.
There might have been something about sarah going back to find jareth and save him, creating a new labyrinth in exchange for her imagination.
Anyway, it’s been a while since I’ve been looking for it, please let me know if you know the title or have any information about it!