Petra...I don't think it will take 40 years before the area of Laguna Hills that slid is rebuilt...it may be more like 2 years. I don't know what the site conditions are, or the laws, but it may be possible to spend millions of dollars and stabalize (sort of) the landslide...maybe just move all the sand out, compact whatever soil is compactible, then build in the hole that is left. The problem is that then you may have the neighbors sliding into the hole (I exaggerate). You might want to look up Portuguese Bend landslide on Palos Verdes....still moving after some decades, but not very fast. They partly stabilized it by pumping out ground water. Not a good idea for everyone to water their lawns...that may be what got some of these old slides re-started.
Chris