Pet location/status not deleted on despawn
The location and activity of pet objects look to not be deleted when de-summoned.
This has an effect on 2 areas of gameplay I have found so far.
First, when a pet is in the quickslot bar and despawns because combat is entered, the next click of the quickslot bar will not summon the pet, but cause a "flash" spawn animation where the pet was previously located when combat was entered. (aka it is de-summoning an already de-summoned pet.)
Second, the player seems to remember the location of ALL de-summoned pets until your character logs out. To see it in action, again add the pet in the quickslot bar, then spam summon/desummon it. You will notice more and more "flash" animations as you continue to do so at the locations of previous pets.