If someone discovers a free, unlimited energy source, launching a 51% attack would be just a matter of seconds. And that is exactly what has happened.
Lol
If someone discovers a free and unlimited energy source the world as we know will cease to exist. The whole world will change, and many things that we don't even dream of will be possible (like sci-fi movies). Bitcoin and PoW would be the least of our problems., and would possibly be a solution.
The Solution
PoW is a failure. PoS is a better system. With Ethereum 2.0, Ethereum is slowing moving to PoS. The threat of someone having massive amount of electrical power is eliminated in a PoS system. As soon as the news breaks out, Bitcoin price will plummet. PoS and Ethereum 2.0 is the future.
PoS was not even tested in a decent blockchain. Ethereum is struggling to get a few blocks minted with PoS. There are many problems with it, such as centralization and economic issues. There are also many unkown future issues.
pow has been tested in bitcoin for 12 years, with 100% success.