This was already answered. Full nodes can veto the miners at any given moment. All of the miners investments can instantly become expensive useless liabilities if the economic consensus of full nodes rejects the miners longest chain.

I will give you two possible scenario's of how this can occur-

1) In the unlikely event Classic convinces 75% of miners to HF, their are multiple extremely large investors* who have made commitments to dump their classic coins and keep their original coins.(remember a HF essentially doubles the money supply unless there is complete consensus). This high stakes form of attack would quickly devalue the chain with the most hashpower driving miners to the other chain or completely ruining both chains. Others may discount this due to the flawed assumption that this would only temporarily devalue the currency but in reality this attack can be ongoing and be conducted in a manner to create steady and persistent downward pressure on the majority hashpower chain.

2) Their are multiple technical solutions that can be implemented if a miner mis behaves where their double rounds of SHA256 hashing means less or nothing at all by the nodes.  Full nodes simply can change the consensus algo.


* These threats aren't being made by Core or blockstream but other large investors some of which are quite "unstable"


This was also just answered with a specific example. I will give you the benefit of the doubt one last time that you aren't deliberately trying to "blunder" the conversation. 100 nodes spun up on amazon ec2 is less of a vote than one bitcoin core node with BTC in the wallet. If those 100 nodes deliberately break consensus by the owner, or are hacked to break consensus than all the damage they will be doing is misleading the community to how decentralized the ecosystem is(Unless a SPV wallet trusts them). Their vote will be ignored by the other full nodes and not be considered.