If one chain has 10% hashing power, for less or equal to 14 days the transactions could take 10 times more to validate. But that's assuming markets aren't correcting miners in the "right" direction in the meantime. Who wants to waste electricity on undervalued coins?
----
Considering most of BTCs have been mined at the time bitcoin core had no competition; I'd say BTC rich people would tend to side with them. Because of emotional attachment, economic ties, and most importantly the dumb but very real reason of software maintenance.
I don't know if non-miners also check the difficulty or difficulty calculations, but if they do, even the minority chain can't fork without affecting existing users.
In that case everyone would need to fork in which case you're back to square one: what to do with the users that can't or don't want to fork. And if you need to fork anyway, it makes little sense to go with the minority chain.
In the end, miners mine what people buy. It's that simple.
Any speculation as to what happens if all miners move as one, motivated by ideology instead of economics, is just that.
BTC rich people are on both sides of the debate, expect to see some dumping all around as they make their positions known.