They will have to fill the portion of it where the spillway has to bridge back over the top of it and enough of it to keep to spillway supported. What is left could certainly be named Moonbeam Canyon but somehow, I think the Department of Water Resources for the State of California won’t sign on to naming that geologic feature in that manner.
The only thing that might help is to get reporters calling it that in questions. Or to get them asking about it. “Hey, George, what is this Moonbeam Canyon we keep reading about?”
I think we here will always call it Moonbeam Canyon. I suppose if enough of us did that, it wouldn’t matter what the DWR called it.