If you take emotion out of this, the version that reaches consensus first, reaches consensus for everyone. This happens every 10 minutes already. Joining the consensus opionion is part of the protocol.
Scenario: 75% miners adopt hard fork and it happens, 25% disagree. How can they reach consensus for "everyone"? This does not make sense.
On paper, why sould anyone leave? This is how bitcoin is supposed to work.
A lot of people will leave. However, maybe more would join. Who can know exactly what is going to happen?
75% is often seen as a majority vote. If you are in the 25%, would you not consider it a fair vote and your view is in the minoirty? In any event, the level to be reached to achieve consensus is evidently the first thing that needs consensus.
Who knows what will happen, but as long as Bitcoin remains internet money, it will continue to evolve. Who knows, creating more capacity to expand its attractiveness may bring even more people into the development community.