Welcome.
After rooting, you can find a ROM that may be out there that has all of the KitKat stuff on it.
Usually a rooted device is no longer "on the grid" so your carrier would not be able to communicate with it to do any Over The Air (OTA) updates, if any.
If the update fails, it will be because the phone is rooted. Updates shouldn't continue once they can obtain root permission. (It could brick the phone.)