I think it is already too late, they have taken a decision that i can't see them going back on. Ethereum will remain centralized and there is little to no chance of them returning to POW or becoming decentralized again. Big centralized exchanges like Binance and Coinbase, and also Lido which is staking protocol somewhat control the Ethereum blockchain because they are the biggest node validators by a long mile.
There's a lot of money at stake, so don't count on ETH becoming decentralized ever again. It's unfortunate, because the project stepped away from Vitalik's original vision of building a "Decentralized World Computer". At least, we have the original Ethereum blockchain by our side (Ethereum Classic). This last one still uses PoW as its consensus mechanism with a deflationary model just like Bitcoin (no more than 210m ETC will be mined). If the PoS version of ETH dies, ETC will carry on with Ethereum's legacy for the forseeable future.
With that in mind, there's no reason to be worried about Vitalik's death or disappearance. The project is open source, so anyone can "thinker" with it and make a new chain if things go south. Who knows where the community will lead ETH to? Just my opinion
