Death

Death is defined by Wikipedia as "the permanent termination of the biological functions that determine a living organism".

The success of an assassination mission is determined by the death of the Sue or Stu. This is why Jay Thorntree and Acacia Byrd were called up to the Sunflower Official's office after handing over Arwen Sue to the Discworld elves; as Discworld's elves take their time with their victims, she showed up on surveillance as technically still being alive.