Developer is, in all modern machines, a roller. It lasts almost forever - far longer than any home user will use their machine at least.
When it does run out, I don't think it's due to wear or the metal particles being 'used up' in any way, but instead because a layer of dirt has stuck to the surface of the roller, so it is no longer any good at transferring toner.
When it does run out, I don't think it's due to wear or the metal particles being 'used up' in any way, but instead because a layer of dirt has stuck to the surface of the roller, so it is no longer any good at transferring toner.