First not everyone is eligible to get a cochlear implant.
To be eligible for a cochlear implant your hearing loss must be really severe and the hearing loss must be severe enough that it interrupts any spoken communication.
You'll only be able to get a cochlear implant if you have no other underlying medical conditions that could cause any risks so if you do get a cochlear implant there's no risk associated with the cochlear implant.
However do note that cochlear implants don't always work for everyone.