One could interpret that differently, It's stuck to a nerve ending, no? That connects to the brain, so in a way its attached to the brain.
The electrode array isn't attached to the brain or stuck to the nerve ending: it is threaded through the cochlea and placed very close to the auditory nerve, in relation to the nerve fibers responsible for transmitting speech sounds when stimulated. Individual channels are said to 'fail' or shut down if they are in a position where the electrical connection can't be made from electrode to nerve fibers. Often it's not so much a 'device' failure, but a surgical placement issue that can cause the electrical stimulation not to happen.
My daughter has one channel that was determined not to be transmitting on the operating table. Doesn't mean the CI is 'broken', but simply that this electrode, this channel, isn't in place to send the signal as planned. So, that one was shut down and another programmed to pick up the sounds in its place. Impedance -- or measure of the signal -- for each channel is tested at each mapping. If too many (I think it's ~ 7 or 9+ channels, but there's some magic number used) are no longer sending signals, the sound quality is so greatly reduced that's it's considered a failure -- because the quality ends up being much like some of the earlier generations of CIs that people often refer to online as being examples of what people hear with CIs.
It's pretty common for people to experience these channel failures, and yet, like my daughter, to still have extremely good access to sound. When the whole device shuts down, that's more rare and requires reimplantation, rather than just adjusting the programming.
A study or data that details results at a particular clinic or hospital, as well as results specific to particular types of CIs, such as this one referred to, is very important. A friend who is a surgeon and I reviewed similar data at two hospitals we were considering, as well as results for individual surgeons, and we chose our clinic, and our CI, and our very experienced surgeon intentionally, looking at such outcomes.