My 2c on the matter - just a warning its going to be long-winded.
After hearing Doki's final statement on the matter again, I must say, that lawyer is worth every penny. Gave enough information to appease the masses, but not too much that it may be used in court against Doki. In particular, being extremely vague by who exactly is the source of harassment, but still say it was just the culmination of multiple instances that ultimately ended with an attempt. Of course, if Doki actually denied that livers were NOT part of the harassment, then it would save a lot of grief the current line-up is currently experiencing from the fans. But considering she did NOT openly deny it, it must mean that's true as otherwise it would hurt her courtcase if indeed harassment was coming even in part due to other livers.
That said, Selen saying "Please feel free to reupload [Last Cup of Coffee] since a lot of money and effort was done by so many dragoons" was super dumb. Sure, she may not have been in a rational mind at that point, as she has made zero profit for the past year and was probably hoping this song + everything around it will put her in the black, but I remember even I had to do a double take when I first saw that tweet. You can't just say to the public 'Management decided to private the song, but ignore them and reupload it anyway', as that is insubordination at best, and outright company sabotage at worst. Sure Selen had acquired rights for the song beforehand from Lily and the producer, but considering how draconian Japanese IP laws are, I can't fault NijiEN for wanting their seal of approval so it complies with JP laws before uploading it. If Selen wants to release things under the NijiEN umbrella, then she has to play by their rules no matter how bad; else its just better to quit. Uploading this video without their explicit consent is already grounds for a heavy reprimand, but openly asking others to reupload a video that has pretty much the ENTIRE IP of NijiEN in it is grounds for termination.
That said, them only knowing about the cover's existence on Dec 24 is absolute hogwash, as I've heard reports that permission was given in writing about a year before (and not just a mere thumbs up from lily/producer). If they only knew about the existence on Dec 24 despite Selen acquiring written permision for it before hand AND having all the legwork and assets done for the MV, then it shows that management is grossly incompetent at best for not knowing the activities of their liver, and actively malicious in preventing her from releasing at worst. That however is another issue, and unrelated to whether or not NijiEN had proper grounds to terminate Selen.
Of course, in the end, it's NijiEN's own rules and their own greed that comes back to bite them in the end. Because Selen asked the public to reupload an MV that has their entire IP (grounds for termination), and because of greed they don't want to fire their top female earner (or close to it), they have to have Selen retract her reuploading statement. They don't want to lose their top (or one of the top) female earners, but they certainly can't have their IP unlawfully spread in the internet being actively encouraged by one of their talents.
What baffles me is that NijiEN even knew what the proper course of action was. They state that "we sought to either publicly disclose the reasons for making the music video private OR have Selen Tatsuki disclose them herself," emphasis mine. We know that Selen was in the hospital on the 27th, which means the attempt was made later on the 25th or 26th, so Selen was in no capacity nor should be in any way shape or form on the internet. So instead of making an official statement, or heck, even ghost write in Selen's twitter, they chose to ambulance chase. If they only asked her once, I would have given them the benefit of the doubt, but their own statement reads "despite FREQUENT communication with her emergency contact" (emphasis mine). Jesus H Christ - that may fly in Japan, but while IANAL, in Canada an employer that constantly attempts to contact a hospital patient for a non-urgent (as in life threatening) reason is capital H Harassment.
Which in turn exacerbate the permissions issue. While Selen still is in the wrong for asking the public to reupload the MV, now NijiEN's practices are put into question. After all, if NijiEN isn't above harassing their livers while they are recovering from an attempt, how can we believe they weren't being actively malicious in denying permission to post the MV as a previous occurrence of harassment? (We know Doki's state of mind was because of multiple incidents, not just one)
And the worst part? I have not heard from NijiEN one word about wanting Selen to fully recover in public, nor AFAIK have any livers made any words of well wishes despite them knowing she was in the hospital. Not ONE WORD as well when Selen said she was released from the hospital; I would love to be stood corrected if one of the livers congratulated Selen on leaving the hospital in one of their streams. But as it is, I can only think that either NijiEN made a blanket ban of its livers even mentioning the hospitalization, or no one cared about Selen to do so. Both prospects are extremely grim even outside of harassment standpoint; like seriously, someone ALMOST DIED here. The most warm we got from the livers was from Ren Zotto's "Very unfair situation, I'm really upset" after the termination, and even then it's vague enough that it can apply to just the situation as a whole.
(Speculation, but I suspect the "was being harassed by other Livers because of mismanagement" may be in part because of this. Blanket ban on talking about the hospitalization may have also included a ban on asking or wishing well on Selen's well-being directly, but I accept I may just be talking out of my ass on this one)
In the end though, NijiEN currently under public backlash is entirely their fault. They could have just sent out their own statement in regards to the MV, or quietly let her go just like Doki wanted to if they didn't want anything to go public and settle everything out of court. That termination letter is the absolute worst thing they could have possible done; I mean sure, it lays out Selen's fault, but not only it gives a timeline of their own faults in this situation PLUS not showing any regard to Selen's well-being, but it also implicates every other EN liver to be part of the problem. Which shows that the company is NOT at all interested in protecting its livers, which in turn gives even more credence to NijiEN being a black company.
So Tl;Dr - I believe NijiEN is in the right to terminate Selen, but from their own words, they are still a big part of the harassment before and during her hospitalization. I'm no lawyer, but I would wager that if Selen is currently litigating NijiEN right now, she would lose the termination part but will win the harassment part. In any case, NijiEN's reputation crash is of no fault other than their own
For context and to lay out all my biases, I was subscribed to Pomu, Selen (almost subbed to Rosemi as well), and Enna ever since their debut, but I hardly watched them a year after as their stream schedules times are totally random. (Some arcs like NijiCANCELLED and TSB were HILARIOUS though) I watch mostly Holo Chumbud, as Sana streamed into Gura's timeslot during the early days of council, Irys/Mumei streamed early enough back then for me to catch them when Gura is AWOL, and now most of Advent sit in the EST primetime slot when Gura/IryS/Mooms are mostly absent. I actually wanted NijiEN to succeed, as you don't want a monopoly in any sector, but after their actions (and lack thereof), I can't say they don't deserve what is coming for them right now and I have since unsubscribed.