Some say that the electrodes aren't stimulating enough nerves or aren't too close to the nerves. Prelingually deaf adults who do comprehend speech well with CIs often come from strong oral background and have good speech skills. Deaf children who were implanted at the age of two or younger develop speech and listening skills and can converse on phones very well. Postlingually deaf adults who got implanted fairly right after their loss perform very well with their implants - most of them can talk on the phone. There is so much misunderstanding about nerve regeneration.
Many deaf people reject CIs because they want to wait for nerve regeneration.
The problem is the upcoming promising treatment for paralysis works only right after the accident - it won't do any good once the nerves are scarred or dead. Also, the hearing nerves and the spinal nerves are apples and oranges - they're not related at all. From a biological view, once the nerves are dead, it's impossible to regenerate. It's just like you cannot make the dead person come back to life. The answer is no, they shouldn't - they'd be better off getting the implant now.