Nimi is cute, and I am happy she's back. Also people are absolutely going to draw her vaping people's nightmares in a goth outfit, calling it now.
My money's on her getting burned out or having a conflict with management during the leadup to Breaking Dimensions. During May she was talking about how she wanted to do more dungeon master streams in the future and was planning a bunch of stuff, which to me says that she wasn't thinking of leaving at that point. After the dungeon stream with Justice in Julyish(?), she mentioned that she'd neglected her "holo homework" and had to go without sleep to get the dungeon stream done. She had to move a few streams around during this period because of behind the scenes stuff.
Then she had her 3rd anniversary in August, followed almost immediately by Breaking Dimensions, she took a week break, came back with a single yapping stream, and then immediately went into ENReco, after which she took another week's break. I don't remember hearing about any dungeon master stuff or other future plans she had in Holo after all the events ended.
Bonus Kirin tweet to feed my rrat addiction:
EDIT:
I'm so glad Doki got
publicly shamed convinced into actually getting real dinnerware/utensils/etc. for herself; I feel like eating microwave meals off of paper plates is a natural multiplier to depression. Hope she shakes this off after a good meal and a good night's sleep.