I have been trying to find a story. I can't recall the title,

Luna ends up in the past shortly after her sister banished her, its heavily implied that Celestia drinks vasts amounts and Luna ends up in hiding in what i recall to be some sort of mining town.

I can't recall if the author ever finished it or not.

Edit:I found it https://www.fimfiction.net/story/328178/the-lunar-millennium