We have several people on WhatNext who have been affected by kidney cancer. I'm sure you'll get some feedback soon.
I can tell you that my mom had kidney cancer. (Her user name on WhatNext is moonshell). Her mass was contained within her kidney, she had the whole kidney removed and she's in the clear now. After some recovery time - she's totally back to normal!
Also - I used to work with the National Kidney Foundation (NKF, http://www.kidney.org). You can have a completely normal life with just one kidney. The NKF is a terrific resource and can provide you with any other background about this.
Thanks - and keep us posted!