How about just starting a new coin? Or jumping ship to, say, bytecoin.
That's pretty much what me and my borther concluded would be the end result this actually happened, but then again we're back to square one. Except this time, as BigJohn stated, the pro-Bitcoiners would be billionaires who can use their new-found wealth to fund Bitcoin2/Bytecoin and maybe make its adoption rate a lot faster, etc.