Um, if the entity the buff is on is destroyed, the buff goes away no matter what.
I was under the impression you got memory leaks unless you specifically ended a buff via finish conditions...perhaps I'm wrong but for a periodic action I thought this was so...
I know this sounds dumb (you'd think if the thing is dead, shouldn't the buff be over?) but I could of sworn I saw that described somewhere, even if an entity was destroyed periodic buffs could take up memory...