$70m of that $80m house is the land its on, and that hasn't been destroyed.

It depends.

How much of that location value was because of the views, proximity to LA proper, etc.?

How much of it was due to the types of houses that were in those specific neighborhoods and the type of people that lived in them?

If the "rich and famous" don't return to those neighborhoods and rebuild their multi-million dollar homes, those parcels will be worth significantly less.

generally “most expensive real estate in country” is where profits from apartments/condos is highest, not the other way around

Not up in the hills or on oceanside lots on the Pacific Ocean next to the PCH. I’m no builder, but my sense is, even if the zoning were relaxed, you are at best building like a quadplex. Four apartments are not going to equal an $80M home.

Maybe in the flats of the palisades.