Once they realize later development is still on ETH 2.0, they will move back. Like you said, defi will die.
ETH 2.0 is promising to resolve the issue and DeFi death call is a good contributor.
Defi will not die, that is not even remotely possible anymore, it is in there and will not go away, this is not like ICO or something where coins are created and sold by the teams with a promise of being higher. Sure there are some stuff like that in defi world as well, many projects that just copy other projects and try to make some money from it as well, but the reality is that many only care about the real projects that people use. How are you going to kill uniswap? Pancakeswap? And many other swaps like that?
Those are good and used because you can trade coins from one place to another, and that is why it will not be going away anytime soon. There is nothing we should be worried about in the defi world because it is not only created but also used a lot, the way it is used is the main reason why it will not be going away anywhere any time soon.