Becouse there is activateifused line in destroyandactivate.fpi.
You edit the entity you want to appear on double click and change its name to for example apen1. And set spawn at start to NO, then edit the enity you want to destroy and in its IFUSED field write the name of appearing-when-other-is-destroyed entity wich is in this case apen1.
And you give other entity script whatever you want, like shootwhensee.fpi if its character.
That is not dead which can eternal lie. And with strange aeons even death may die.
H.P.L