My balance nerve obviously had been destroyed long before my GK and surgery. At the time of my VNG testing I was told that I had 90% weakness, even though I never experienced balance problems. Even the ENT upon doing the standard tests had said that my balance "looks pretty darn good". In slow growing tumors the nerve may deteriorate very slowly, in which case the other side compensates fully, without the patient ever realizing it. In these cases cutting the nerve after surgery does not make a difference.
People who usually experience severe problems after surgery are the ones who have a fully functioning nerve, and all of a sudden find themselves with only one working side. This obviously is a shock to the body, and it may take quite a long time to compensate. Vestibular therapy is often needed.
The same people are the ones experiencing problems after radiation. In this case it may be even more complicated, because you may end up with a partially functioning nerve, which is sending wrong signals to the brain. A partially functioning nerve may also be a problem in hearing preservation surgery, like middle fossa, which does not sever the nerve.
Have you had a VNG test? It is quite long, but it is the only way to tell what is the current status of your vestibular nerve.