It's irrelevant as to how many miners are working on the original chain. Mining could be done on a single laptop by one person for all the protocol cares.
Lets say that 99.9% percentage of the miners decided not to go along with a hard fork, and 0.1% did, effectively bitcoin would be split up into 2 networks, A and B.
Functionally, they would be nearly equivalent, ignoring network lag. As a user you could even have two clients, one that accepts transactions for network A, and one for network B. And your wallet in network A could even have a different balance than in network B. So how do you decide which wallet is correct?
The same way everyone else does, by mass consensus, ie. by what everyone else is using. Ex, if you wanted to buy stuff from merchant X, and they had a network B wallet, it wouldn't matter how many miners were mining on network A, would it?
Miners only provide security against a double spend 51% attack and that's it. By their very nature, they also are in the best position to do a 51% attack. Therefore the only leverage they have is they could threaten the new network. But as I was explaining before, if they attack network B, it goes to show that network A is nearly as vulnerable as network B is.
In other words, its as centralized as fiat, which destroys one of the most highly touted features of Bitcoin as a currency of the people. If a couple of a bad actors (ie the people running the mining warehouses), can destroy it, either because of government coercion or by their own free will, then as you can see, Bitcoin is like the emperor who has no clothes. It could be destroyed at any time.
So, we have a MAD situation (Mutually Assured Destruction). If the users force the miners hand too much, the miners could retaliate, by destroying bitcoin by executing a 51% attack. But of course, as long as the miners are making money, they don't want to do that.
Nobody invested in the bitcoin wants anyone to know this, the users nor the miners, because it goes against their best interest to show the weakness of the currency they own.
However, the longer this draws on, the more people will wake up and see that Bitcoin is truly becoming centralized into something that resembled Beenz and Floodz from the 90's. Not a currency operated by the people, but a currency owned and operated by a few large corporations.