I honestly hate worrying about balancing in RP's of any kind, because in the real world and in most fantasy world's, people aren't equal is a fact of life. Usually the villain or antagonist are suppose to be the best, but that doesn't mean that they will win, in fact they usually die in the end. But that's not the main point, so I'll leave it at I wish more people would let people follow the rule 'no god modding' while also not butchering their ideas of their character by being overly picky.

I have written sacrificial lambs before, it helps when you're the GM for a RP, and you have most of the plot written down in your mind before hand. I actually love character death, and suffering. Dark drama is what I live for. And I've never had a problem with writing villain's characters or good characters, meant to eventually die. My fiction usually has wonderful body counts. I'm never been selfish to keep my creation if it meant making the story better as a result. But it's a lot easier when you're RPing with friends.

Depending how you want to write the death, you can as someone already mentioned, create 'death flags' for the characters, though sometimes unpredictability is better than heavily foreshadowed death. It's hard to really hard to say exactly, how I write them, because it varies wildly depending on what I'm writing for. Never make it too obvious or it won't be any fun. I usually tend to avoid deaths that can be seen coming a mile away like being very old or being very sick. Usually making the character suffer and dragging out their struggle not to die, helps add to emotional weight. Though, quick and abrupt can work just well. If you're not the GM or at least the CO-GM of a RP, make sure they know. In fact, I'm actually thinking about doing something similar in a RP, I just joined. But I digress. 

Good luck with writing. :3