This is FUD. If the electricity consumption becomes prohibitive, Bitcoin will just switch to Proof-of-Stake. Ethereum's already doing it. Zero electrical waste.
What makes you think most, let alone all, miners will agree to switch to proof of stake when the miners have invested exactly in proof of work? They’re just going to leave all those machines they set up and walk away? LOL
And even if most of them did — which is already laughably improbable — the ones that stayed behind would continue the arms race. Bitcoin Cash didn’t kill Bitcoin. Why would your Proof of Stake version kill it?
PS: Ethereum’s community and governance is different, and focused on computation, so it has some chance of switching to Proof of Stake. ETH isn’t known as a Store of Value, and in fact is designed to inflate slightly to countract this notion. And yet I am sure that not everyone will stake in Ethereum 2, the ones who stay behind will cop-out to Ethereum 1 being a store of value just like people continue to mine Ethereum Classic mostly for the token rewards. Sadly even Ethereum may have a version of this economic morass.