The cars will presumably fallback to native clusters when the phone stops responding. It’s still too early to tell though, but they are a very safety conscious company so I assume that people have thought about contingencies before making themselves liable.

At the least it likely won’t be worse than the multitude of cars that have moved to digital clusters anyway and may freeze themselves.

The claim of Carplay not working without Siri is also incorrect. A quick Google search shows you can disable Siri but will be limited in what you can do https://stereoupgrade.com/how-to-use-carplay-without-siri/ since the goal is hands free use.

Lastly most newer iPhones do on device Siri processing for common commands so it’s not really a privacy issue.

1. Reverts to the standard vehicle interface

2. Siri is activated by user input (holding a button / pressing a button in-car) with a side feature for hot mic (hey siri) that’s disabled by default

3. Maybe there’s car implementation solely driven by Siri? Hondas is touch screen and Mazda is button/knob based (and touch screen but only when idle).