Mosher
Mushroom dad
I'm pretty sure by the time a corpse has rotted to dust there will be new corpses to replace it. Not to mention they could embalm their corpses to keep them around for at least a thousand years.
EDIT: Of course embalming isn't an easy or cheap task so same problem with the droids, the upkeep of embalming every single corpse the population produces would drive your economy into the dirt.
The way it sounds from Ailed's posts there would be a large population of zombie slaves and a small faction of necromancers controlling it all, with the small amount of necromancers never going to be bountiful enough to fill in for losses.