FWIW, it seems Graphene will let you can remove the Phone permission from the Phone app.
After that (with no SIM) I tried 411 and it says "The application cannot make outgoing calls without the Phone permission."
With the phone permission I call 411 and it starts the call and then says "Enable Wi-Fi calling to make a call."
I'm not sure and don't really know how to safely test if that disabled 911 or not without the Phone permission!