Theoretically the ETH PoW fork will drop in value relative to the original ETH. That would decrease the mining reward and result in less mining (and more GPUs returned to gamers).
The goal isn't to "kill" the coin entirely, the goal is to reduce the amount of mining by 99% or more. And that's an easily achieveable goal. See Ethereum Classic which only uses 1% of the resources of Ethereum because of how low its price is.