Not necessarily. Maps caches large areas, and GPS position is based on the GPS receiver in the phone, not on whether or not there is cell service.If you go into an area with no cell service, then you lose the GPS tracking on CarPlay and Android auto.
I hope Google doesn't kill the Waze user interaction, since Google prefers to use more voice activation than screen interaction.
Stand-alone units are still useful if you're a business traveler. And you can get stand-alone units with free traffic and map updates.