When do they expect PoS will be live at the latest? Before the fall or next year?

At best it will be another hard fork. The miners need to vote on the change to PoS, and why would they? It would render their mining equipment worthless.

It's the other way around. The miners can't do anything to prevent the switch since most major Ethereum users (aka Infrastructure providers) are clearly in favour and are already participating in the POS chain (which is currently running in parallel and without transactions).

When they update they miners are simply cut off.

Furthermore, Ethereum contains a self destruct mechanism that requires a hard fork. Unless miners can coordinate a competing POW fork (and convince rich people that the bad PR and profits for them are worth it) they won't be able to do anything.

Isn't ETC quite clear precedent for that?

It obviously wouldn't be as large and probably suffer from everyone on real ETH selling off their duplicated assets, but it'll surely be a thing, a last ditch effort to keep mining rigs profitable before everyone moves on to the next best coin?

Sure it could happen (and probably will in some form).

However unless it captures a siginficant fraction of ETH value it won't be worth much and in turn won't be attractive to miners.

Right now ETH makes up 95+ percent of all GPU miner revenue and there aren't a lot of (successful) new POW coins these days.

I think the (GPU mining) market simply collapsing has a high likelihood.