I want to address this as it comes up a lot and not just about Kes.
Kes was replaced by 7 of 9. This was done for cynical and OBVIOUS reasons having to do with sex appeal and TV ratings. When an actor is let go from or quits a show, especially a crime or adventure show, they are often brought back one more time to "kill them off." Also done for ratings. Don't ask me about the psychology of that because it's crazy. If you think about it you can find many examples of this phenomenon.
Setting aside Ms. Ryan's acting abilities (she's not bad at all) the difference between nordic, statuesque, busty 7 and Kes is clear. 7 walked around in a corset, catsuit and heels for God's sake, and, without looking, I guarantee you will find there was a corresponding ratings spike. Fair? Nope. Not hardly. But also not based on spite.
At no time do fan letters, even massive campaigns, engender a spiteful reaction such that the writers sit down and say, "All right, you want Kes back, FINE. See how you like THIS!"
It just doesn't work that way.
Deliberately or not, it was a spit in the face of the Kes fans.
And I'm still curious about why a character who they had done everything to erase from the history of the series (she was never mentioned after being kicked out in the first place and the Hydroponics Bay in which she did grow flowers was transformed into some Dracula's den for the Borg who were brought on board. Obviously they had no need for food anymore) all of a sudden is brought back- only to be destroyed in the worst possible way and it just happened to coincide with a letter campaign to bring back the character as a permanent main character again. Not to mention that they actually planned to kill off the character as a not so nice gesture to the Kes fans but Jennifer Lien made them change the end of the story.
Too many coincidents here.
As for kicked out main characters brought back to be killed off, I've only seen that in one case and it was in some police series called "Pacific Blue" where one of the original characters who had eft in he middle of the series was brought back and killed off. The episode was absolutely horrible but I don't think that there were any letter campaign going about that character.
As for the spike in ratings, there was such a spike when Seven arrived but it faded quickly and the ratings for the rest of the series were lower than for seasons 1-3.
So you honestly believe that they spent all that time (conceiving, vetting and writing the story) and money (one million per ep, minimum and likely more in this case for the ep-specific FX) simply to be spiteful towards what amounts to a tiny fraction of their total audience?
No. That never happened. I'm sorry. It just didn't.
People make cynical decisions all the time, largely to enrich themselves, but they don't do things on that scale to spite people they don't know and will never meet.
I'm not trying to burst your bubble (well, not in a mean-spirited way) but isn't it just possible that the people who invented Kes just wanted to tell one last story about her? Or that they liked the actress and felt bad about the cynical decision they'd made to cut her and wanted to do something nice?
Why assume the basest motivation?
If they wanted to do something nice, then why come up with such a horrible and insulting episode? They must have realized that the fans, especially those who were staging a letter campaign to have the character re-instated would never appreciate such an episode.
As I see it, they had two options, to bring back the character as the fans wanted and not bring her back at all. They did choose option 3 which insulted and enraged almost every fan of the character.