By Mikas own words, she currently has NO plans whatsoever. She plans to visit roomie for some time, maybe travel a bit and then take care of her multiple health issues. She obviously has seen speculation online and was more impressed by the plans people come up with, like "wait, i could actually do that" and was happy that everyone sees her as responsible enough to think that she actually has plans.
I doubt this would result in much of a shitstorm. Mika is still fairly small and it is not like niji is trying to keep any of their id livers.
Mika talked at length about why she is leaving in
this stream (around 02:29:00). It is pretty long, but i will try my best to summarize it: She wants to be part of the big events, wants to have merch, meet and greets, all that fun stuff. But since the merge, all of that has become impossible for her. At the same time she has become close friends with multiple holo id and niji en. She sees them getting all this stuff, while she is stuck with no signs of anything ever moving. The charity stream was the last big thing she could achive in niji, everything beyond that is impossible. Not because it could not theoretically be organised, but because niji has decided that they wont do stuff for niji id anymore. She went from "waiting with excitement to just waiting to not hoping at all". Over time, this took a massive toll on her and has now reached the tipping point.
From what i can see, she still likes organising bigger things, for example she did multiple game show streams in the past weeks, but she just has 0 support when doing so.
As someone who considers Mika one of my oshis,
FUCK YOU Nijisanji for treating her this way. The amount of potential they are wasting here is insane. I really hope that, if she returns to streaming, finds a good place to achieve her goals. As for the candidates:
Hololive: Maybe? She is close with a few of the holo id (as in they meet irl regularly), but if she would join holo id the language would be a problem. She currently streams english 99% of the time, so if she were to speak english all the time in holo id people would (understandably) get mad, but if she speaks only indonesian none of her current viewerbase would transfer over. Holo en could be a possibility too, but i doubt it.
Vshojo: The most likely option imo. Mysta and Nina are already there and she is also friends with Geega. I could imagine that while she herself would not apply to them, that her friends could have Vshojo reach out to her and ask her if she wants to join.
Phase: Im not that deep into Phase, so it is hard to judge. Given recent statements, does Phase have anyone similar to Mika (chatting streams with very high chat interaction)?
Idol: I don't know much about Idol, so maybe?