In my case the tumor was medium to large and they suggested it had probably been there for up to 10 years (a guess).
I was not aware of any balance issues pre-surgery (although in hindsight i do recall a few instances of walking my shoulder into the side of the doorframe at the kitchen at work and i guess that was odd enought for me to remember).
I passed well the basic (heel to toe) testing all the docs put me through, but did struggle when eyes were closed. I didn't think much of that though.
I did some more comprehensive balance testing at the ENT's clinic at the hospital (e.g. they put sensors on my head an i had to do a bunch of things, like watch lights, shake my head; also they rushed warm and cold water into both ears). These were meant to test for dizziness, beyond what i could comprehend on my own. I was told that there was some LACK of dizziness on my left (AN) side during the water test. I guess this indicated that there was some loss of function, and I guess the right side was picking up the slack as like i said, i didn't know i had balance issues.
After surgery, the first week (in hospital) was rough, but i barely got out of bed, except to pee and after a few days the PT suggested I get up and do a bit of walking and sitting up in chair. I ditched the walker i rented for home in a day, and managed fine using walls and hand railings and shopping cart at the g.store, but really i didn't feel so much dizzy, just out of sorts (not sure if this is the 'wonky head' to which so many refer, but for me this was temporary and really just a stage i passed through in the early weeks post surgery), which i would expect after that kind of surgery/trauma.
I really did not feel that my balance was compromised by surgery. The only thing i am aware of now is that if i am walking fast and turn my head (to look for bus coming), i misstep a bit. I would say my balance is 95% or better, it is not an issue at all.
I also asked about whether the nerve could be saved in surgery and was told no, pretty much for reasons Steve indicated. I figured their the experts.
good luck!
Trish