I think it can be a good thing the Ravencoin's halving, if the price goes up it can easily compensate the halving.
All the other proof of work blockchains minable with GPUs are very small blockchains compared to Ethereum blockchain. When ETH will be proof of stake you will see all the hash rate get distributed and moving regularly from one PoW coin to the other but yeah I'm pretty sure the profit will never be as good as now.
My bro is a software engineer working for a DeFi company and he explained to me lately the latest developments in the Ethereum world and frankly these PoW coins like Ergo, Ravencoin etc. are simply not in the train in terms of future technology. Almost everything is happening on Ethereum blockchain (lately it's the Layer 2 boom
https://l2beat.com/), the PoW coins are simple investment vehicles. Even Ergo doesn't have a lot of resources for coders, the vast majority of developers are on Ethereum.
Cardano coming soon will be interesting to follow because it will be possible to have your own blockchain... let's see. Pretty amazing concept that I don't understand all the details for sure hehe.
I don't think PoW coins will disappear. Monero will be relevant for a long time.
But the further situation with video cards after Ethereum mining is very interesting to everyone.