Well, that's not exactly accurate.
If a hero is wounded badly enough in battle, he will die. No other wounds will kill the hero, and if he survives the battle, he will not die of the wounds, no matter what.
Because it is based on wounding in battle, there is no set percent chance of death. It is based on a variety of factors, including but certainly not limited to the unit commanded, the size and composition of the enemy force, and the hero character's age.
