Risks

These aren't the things that worry me most.

Probable lose of any residual hearing in implanted ear.

Anesthesia: rarely, death. Possible loss of teeth or laceration of phahynx do to trauma from endotracheal tube insertion

Possible injury to facial nerve, resulting in paralysis of the face on implanted side.

Possible injury to the taste nerve, resulting in loss or change of taste.

Possible balance problems, vertigo, dizziness.

Meningitis.

Longer term: 

Device failure requiring revision.

Ossification in cochlea or auditory nerve.