Oof
this is a big loss for Niji. She had an amazing voice.
IMO Melissa's voice is is honestly too good for Nijisanji. Or any sort of corporate vtubing gig.
A lot of vtubers sing. Some of them are known as being especially good singers, and even get record deals, MVs, concerts, etc. In my opinion,
most of these people (excluding ones in vsinger specific agencies) are not "good enough" to have achieved or maintain such success separate from vtubing. As an example, as good as they are, I don't think Higuchi Kaede or would make it on their own (feel free to flame me, Kaede and Suisei fans). They owe their success in large part to the agencies they are a part of, and if they were to leave I don't think they'd maintain that level of success in the long run.
Nijisanji definitely helped Melissa get out of the wagie life, so corpo vtubing was not a waste of time for her. However, IMO Melissa
is one of the vtubers who can make it on their own. They should be in charge of their own IP and be able to produce songs that are not owned by a corporate entity that can fire them at any moment. Obviously Melissa could do this on the side, as Demondice/Calli does, but I don't think she's really gets enough out of vtubing to make that sort of double life appealing (and lets be honest, it probably only works for Karen because she's a workaholic).