I hate to nominate one of my own characters but
Erisha Da Hadez death in The Colonies was a doozy.
Spent a couple of years helping fighting and winning a war, annihilating the enemy realms. Key in negotiating the joint creation of a new realm from their territory with nobles from allied realms. Arrives in the new realm for the formality of being appointed ruler.. immediately slain in an accidental battle against the new realm caused by a newbie player forgetting to move from aggressive to evasive when returning home.
For extra cringeworthy irony points that player is my real-life wife.
