It's all a matter of opinion, but yes, in this case they should get replaced imho. Human staff should watch over it and refil the shelves and such..
You replace the cashiers you might as well replace the shelf stocker because you no longer will be offering social interaction with the customers. Its a slippery slope and I think most people understand that you need to defend the human aspect or lose it all together.
Having worked in customer service side of things as a kid,I realize the importance of having people available in a store.
You leave it to the shelf stockers to help and they will never finish stocking the shelves.