How decentralized is ethereum?? Or is it centralized before Vitalik merges with PoS?

What makes ethereum decentralized? Does that mean miners will continue running the program as it is today if the PoS merge happens in 2023? Will Ethereum users split their coins when the merge/fork happens? Will some users prefer the $4000 ether coin? Or will the PoS Ether coin be more or less valuable than the PoW?