It is not gone for good, I can still keep the back camera up while driving.
I had some problems with my car, so I installed the V 9 update. I leave the camera in upper portion most of the time. I do not look at mine constantly, but I am driving an Model X with a lousy rear view mirror. I asked about the rear view mirror on my test drive and was assured I could always use the back up camera, which has now proven invaluable. I would never have upgraded if it had not been allowed to stay on all the time. Not sure why Tesla forgot they publicly stated the Model X would always be able to use the camera as a rear view mirror--but it was stated several time from 2016-17 on several sites, threads, and I think even on Twitter. I am not on Twitter, but I remember someone posting one about someone complaining about the Model X rear view mirror---and it was answered with--use the back-up camera.