Each person must decide for him or herself if a CI is right for them.
In my case, I had nothing to lose and everything to gain. If I lost what very little residual hearing I had (which I did -- I'm completely deaf without my processors), I could still continue using the same communication techniques I had been using prior to my CIs. For this reason, I went ahead with the surgery and have absolutely *no* regrets.
Prior to my first CI surgery, I had several discussions with my surgeon and audi about my prospects for success. Since I had over 20 years of auditory memory, both my surgeon and audi felt my chances for success were quite good. As it turned out, we also discovered that my blindness played a significant role in my success due to the fact that I already knew how to use my hearing for orientation and daily living tasks, so learning how to hear with my CI came (for the most part) naturally.
For those considering a CI, I encourage you to do your research. Talk to a CI surgeon and audi at a qualified CI center about your hearing history to determine what your chances of success will be. (For some people, success means being able to hear environmental sounds while for others it means being able to talk on the phone.)
Talk to other CI users with a similar hearing loss/deafness background about their experiences.
Most importantly, have high hopes and low expections. Do not expect to hear perfectly when your CI is activated. Learning how to hear with a CI takes patience, persistence and practice (what many CI users call the "3 P's").
Again, each person must decide for him or herself if a CI is right for them. In my case, it was the best decision I've ever made!