That is powerful, polite, and yet shows the "fit of anger to regain kibun" that sounds like it's acceptable according to the OP and related articles. It also is deeply shaming, coming from an "old woman." (Characterizing it that way makes you both vulnerable and yet venerable-and-wise.)
I have not shown the best of judgment in some of the things I've suggested or thought were clever in the last couple of days, so I want to take a bit of time to think on it, but I think it's a good move. I also think that getting a strong, solid hint in there or via some other avenue that this will get wide public release should CoH/V actually finally close down would be utterly terrifying to the CEO of NCSoft. I think, based on my extremely limited knowledge of kibun and asian culture and PR in general, that you've found a masterful way of hitting them with a shame that could force the directorship of NCSoft to retire if it became public.
What I write here is a probably poor suggestion, but perhaps some variant on: "Because of the gravity of this to me and those I have named whose sorrows lay at your feet, it is imperative upon my own honor that I be certain you have seen and understood it. No private response will be sufficient; I cannot be sure it is you who have sent it. Therefore, should no action be taken to restore the harmony you are casting to the ground to splinter into ten thousand irretrievable shards, I will make this plea in a public reading of this letter on channels and venues I know you will be unable to miss."
That's clumsy and too openly threatening, I think, but if that can be reworked to fit the rest of the letter's tone and be a little more subtle (so nobody can point to it and scream "extortion!"), I think that we should try to get the sentiment in there.