The miners are not the only stakeholders. What really matters is whether the users want to own the new coins or the old.
Nope. The consensus is very clearly defined. Users of coins have absolutely nothing to decide in this decision making process. If you want to understand how Bitcoin works I would suggest to study the whitepaper. If a switch to another algorithm would be possible, bitcoins would be worthless bits. The most important feature of the network is that some elements can't change, first and foremost the money supply and proof-of-work. You can ask some of the miners and core developers how likely such a switch is.
Nope. A cool part of the crypto universe is that
anyone can fork the coin (considering he has the majority of the shares/consensus AFTER the fork against hostile groups) to do whatever, and the markets decide if the fork has any value.
I don't believe miners and core developers would like to support such a change, but unless they have the majority of stake
in the fork, they don't count. You can decide the parameters of the fork such that they actively suppress the position of devs and miners. Just like you would be designing an altcoin.