I have killed characters for the sake of RP one time, though as far as I remember, their deaths were not explicitly mentioned. I do not even remember if I played the same band of characters again, so I am not sure if anybody in the RP knew that some of them died, but I clearly remember that I have used a method to decide if certain members of a team were dead. I have also killed off main characters of my writings, in fact, several of them have died in a rather anti-climactic way at the end of my largest narrative yet. However, I do not think I have killed off a character who was the core foundation of my stories yet, who seemed to be of key importance. Yes, I have killed protagonists, but not the very pillars that the story rests on, or I have killed them at a time when it did not matter anymore.
As for character death with actual impact on the story, I do not think that I have done that. Most of my characters tend to survive until the very end and only the more minor ones get killed off early on. I also have not killed a serious, named character on-screen in an RP yet, which I am sure I will remedy some time.