Nerves connecting with hair cells emerge from the Cochlea as the VIII (Acoustic) nerve.
I would not anticipate, however, that an adult who has been deaf all his/her life would benefit much from a cochlear implant.
Such individuals would not have developed, nor would they be able to as adults, the necessary perceptual neural network to utilize any sound that was received.
The cochlear implant feeds directly into the VIII nerve, the nerve of hearing. But how does the normal cochlea relay information to the brain?
We described the Sensory Neural Unit as a hair cell and the nerve that connects to it. In principle this is true, but in reality, the system is more complex than that.
Many nerves connect with one hair cell, and a nerve will connect with more than one hair cell.
These nerves connect with the base of the hair cells and then transverse down the core of the cochlea were they emerge in a single bundle (trunk) called the VIII th (Acoustic) nerve.