(If you're not familiar with this in the context of renewable energy, then you might want to google for news stories on what the long-term drought in the western U.S. is doing to the "sure thing, forever" supply of hydroelectricity at many of the major dams.)
The environs of Hoover Dam are exactly as safe today as 10,000 years ago, and will reliably be as safe 10,000 years in the future provided no nukes blow up upwind or upstream.
Solar panels floating on the Hoover Dam reservoir will happily produce as much power as the dam at full tilt, with enough left over to pump water back up to it for overnight use, reduce evaporation enough that water drought will be substantially less problematic, and provide power for desalination besides.
Floating, water-chilled panels will last at least 50 years, by which time they will likely not be needed anymore.
Such disasters should only be a small - if bright red - footnote to a good policy: "NEVER build anything resembling this historic disaster. And if anything ever shows operational characteristics remotely resembling it, then shut it down IMMEDIATELY."