Despawn option

Hi there!
i am looking for a special kind of "option"..

i want a mob to despawn when nothing happend to it,
but if it gets hit by another player (or something), it will never despawn again,
unless a special triggers happens..

is this possible?
any kind of support is welcome Image may be NSFW.
Clik here to view.

(sorry for making 2 threads in such a small time, but i reallllly need it, and i can't find a solution for it)

thanks
AnimalMace