K'Ehleyr used to be a favorite character of mine. In fact, we named a parakeet after her. It was nothing about the species; just an honest homage.
Anyway, I agree w/ everyone. While it would have been nice to keep her, her death was shocking and made Reunion truly outstanding when we see Worf's reaction. And, as DGCat wrote so well, it became fertile ground for so many more good Klingon scripts.
BTW, I met Plakson at a convention many years ago. As with many people, she was even more stunning in person than on the screen.
Edit: Oops, I forgot one of the main points I wanted to make. I guess I've changed a lot since TNG was first aired. Although I originally loved the 2 K'Ehleyr episodes, when I tried to watch "The Emissary" again a year or so ago, I found Plakson's acting to be annoying.