I would also agree that mechanics arent at fault, but I do think the publicity of the rules (oe rather, lack therof) bore some fairly major responsibility.
Ultimitaly, I think the issue itself sprang from the loss. Some people can't stand losing, but I suspect that was probably a minority, or at most a plurality, of the people upset. Fundementally, I think that the reason is that people care. Poptart writes some great characters, and I know I'm not the only one who strongly empathizes with Kakara. It's not a freindship, but it's not entirely dissimilar; it's that same feeling of kinship you sometimes get when reading good books, and you come to relate to the characters. When you see them get hurt, that hurts, and when it's someone you can't stand doing the hurting, that gets you more upset, and Dandeer totally qualifies here. In serialized work, you can't just continue to the next chspter, and go on until it ends, but under normal circumstances they still end up pretty fine. This leads me into what I beleive the culprit is, and why publicizing the rules helps: blame.
When people get upset, an unfortunate but natural response is blame. Blame itself is... not ideal, here, but it's mostly tolerable, and it's a price of doing business with human beings when stakes are on the line. In a book when something bad happens, the blame tends to go right onto the charachters, with the author as a distant second and largely harmless (people read during their ordinary life, far enough away from the author for any blame to run its course) - human minds are great at anthromorphising stories, so even if PastryMaster is the one controlling the charachters so that Carrot Wukong gets in trouble, they'll blame Reednad, the evil warlock who did it. This is a good thing. Role playing games also tend to have additional targets in the form of dice / rng; the fact thta the loss of an invested charachter is more personal is balanced by the fact that the dm can rightfully say, and easily prove, that really, he doesn't have it in for our intrepid carrot, that's just the way the die rolled. This is where our thread troubles began.
After the update dropped, things might have gone almost fine. Many, like me and the others still in this thread, could accept the result even if we didn't really *like* it, or could control our frustration. Others, like my brother, left the thread for a while because they wanted to acoid what might happen if they didn't. Blame starts, people start self flaggelating and some accuse others or go I told you so:; recriminations, but not enough to boil over. The decision not to vote break, while reasonable from a time prespective, could have been much better handled, and added to it. Ultimately, agency and railorading enter the discussion (they definitely would have anyway, but I dont think it would have been to the same extent), and when the blame heads the author's way Poptart is the only target. Instead of being able to point to the dice or the rules that are against them, it comes dosn to their anger vs how much they trust poptart as a GM, and when the answer starts to become the former to any real extent, a feedback loop forms.
Ultimately, I don't think this will solve the issue of salt and upset players. That's further up the chain, and will form before this comes into play. I do think however, that this will reduce the scale, and in combination with the effects of the modpost and (hopefully) some of the worst offenders leaving, nothing like that previous occurance will occur.
We also aren't limited to one option. We can have public rules, and rolls, and contact a staff at updates likely to induce salt, and we can learn from our mistakes. Even if this isn't a solution, it's part of one that's already largely in process.
Obviously, some of the obovr is supposition; I took a small sample from each group that I knew, and then assumed each sample was completely representative and used that to create a universal solution, which is a famously reliable strategy that has never given a bad result before.