Does " a willingness to do so" mean " a willingness to sacrifice his life for his cause (of democracy)"?"His was not an active decision to die, but a willingness to do so"
It is impossible to say. The original "His was not an active decision to die, but a willingness to do so" makes no mention of sacrificing his life for a cause. The only thing we can infer from the original is that he was willing to die.