I have a friend (who I lost touch about 2 years ago
) who was implanted about 5years ago with a CI.
She had only very mild balance issues pre-implantation, however unfortunately since being implanted she has had some major balance and vertigo problems - that appear to be permanent.
Last that I heard from her the balance issues have improved somewhat and she does much better during the day now, however at night she uses a cane because her balance is bad enough that she was tripping, stumbling and even falling in the night.
The problems at night/ in the dark are because she has to rely more on her eyes to help her stay balanced and of course it's harder to see the ground clearly in the dark.
I haven't talked to her in a while - however as far as I know she's still having issues.
She has said that even when her balance problems where at the worst, that she's glad she went ahead with the CI - and that for her lifestyle the balance problem was a small price to pay for the hearing she gained.
FWIW her situation is more the exception it seems than the rule. I would strongly recommend that you talk to some Audiologists, and Drs who specialize in both
CIs and Meniere's to get the most accurate answers you can regarding outcomes.