Elephants are free ranging entities, not herded or bred. Humans have little control over their existence. As such, they do not respond to the same premise as domestic cattle, etc. They do not bread in greater numbers as their stock diminishes, they just become fewer, and fewer.
Of course that would happen if no one gained control of the animals.
But people already have put herds of them together all around the world. If their meat becomes desirable, or their ivory becomes legal to sell again, more and more herding will occur, and their numbers will increase.