>Meanwhile, there's no technical way for the miners to keep the switch from happening.

Right, because it’s never happened that miners disagree with a change and split into a different chain…

They can certainly do that, but that doesn't keep the merge from happening. It just means there might be a PoW chain on the side. It'll be up to the market to decide whether it's worth anything, and if it's not worth much, it won't support much mining activity.

So far, the miners don't appear to be organizing a chain split. And it would take some organizing; they'd need to defuse the difficulty bomb, get exchange support, try to get support from the people running tokens backed by custodied assets, etc. Perhaps most critically, they'd need to get a large portion of the user community to believe that PoW is better and worth sticking with. That's not happening either, and Ethereum users are very much looking forward to PoS.

Remind me how many existing splits there are?

One. In that case, unlike today, a large portion of the user community believed that the alternate approach was a better idea.

And the market did make a pretty definite decision on the two forks' relative worth. ETH today is worth $2800 and ETC is at $26.

More than one, but alright. The point is the mechanism exists to just fucking ignore PoS and if miners don’t think there is enough in it for them, it won’t happen.

Of course miners can keep their PoW chain going. That doesn't mean anyone else will care about it, or that they can stop the PoS chain from going live.

There have been lots of Ethereum forks, but ETC is the only case where the old chain stayed active. In every other case the old chain was abandoned. (Bitcoin on the other hand has multiple active chain splits.)