In other words, they're free to do what they want, just as they are now; free market. If you're suggesting that sticking by their guns would become an exercise in futility, that's just the way life works: You can't always get what you want.
I don't think that the right word is choice here. A choice would be agreeing to a proposal between two or more. This is more of a ultimatum, either you join or you quit. Mining on the old and slow chain is pointless though.
the most possible scenario is the rest 25% to keep running the old bitcoin system and to change the mining system and ban asic miners. And i am very sure that for many months we will have two crap coins with no value at all and with 21 supply coins each other.
Why would the remaining miners agree to make their equipment invalid?