If they’re still connected (exitnode mesh or otherwise) and the target domain is no longer maintained by auto manufacturer, then someone else can grab the domain, register it, and the cars will try to connect. Maybe I misunderstood your meaning, but saying a mesh is slow or inaccessible is inaccurate. The whole internet is one giant mesh, and it works fine.
You just described about 60% of the internet. It’s infuriating it came to this.