I understand the bitcoin holders can just sell and move to another chain/coin, but a mass exodus would effectively destroy their stored value as there will be way more sellers than buyers. So the miners can essentially keep doing what they are doing as long as they don't bleed off too many users.
If bitcoin would change its algorithm, it will lead to fork. Miners will stay on old fork. Some people will move to new fork. So there will be two bitcoins used by two communities. Which fork will be used by most people is questionable. In the end USD/BTC is all that matters. I don't really see majority of bitcoin users migrating to PoS, but I might be wrong about that.
What’s more likely to happen is to have users fork off to a different PoW algorithm or even PoS, rendering the mining equipment of miners useless. If the economic majority of users run the new fork software, the network effects and value of Bitcoin gets preserved. This is how the segwit movement managed to pressure miners into activating the segwit soft fork.
I understand the bitcoin holders can just sell and move to another chain/coin, but a mass exodus would effectively destroy their stored value as there will be way more sellers than buyers. So the miners can essentially keep doing what they are doing as long as they don't bleed off too many users.