No one will swap or collect your ETH or take it for vanishing. Just an upgrade to improve the ecosystem. Ethereum network is becoming very expressive for transaction fee.
and base on what he said you don't need to be afraid if you just stay your why in your wallet.
As I understand in upgrade ETH will move to pos which is you can earn ETH by staying it on your wallet.
How big it is depends on how many ETH you have.