To most people, brake-by-wire means totally electronic control. Tesla's current models are only electronically assisted (in that there is an electrically powered hydraulic pump). There is still a physical connection between the brake pedal and the master cylinder. This means you are still available to provide some braking force if you loose 12v entirely.
I was worried about the idea of a fully electric braking system because of the failure mode you mentioned. It looks like hydraulic brakes are not ubiquitous.
"Some Tesla vehicles use hydraulic brakes, but not all. Recently, Tesla has equipped its cars with a full self-driving system. Tesla’s latest car comes with full-electric Brembo brakes. These brakes use electric actuators instead of hydraulic fluid pressure to actuate."[1]
I'd be curious what mitigations they put in place regarding an electrical system failure.
The mech4cars.com article is conflating the service brakes and the parking brake. The service brakes (the primary, foot-pedal actuated brakes) in a Tesla are hydraulic. The mech4cars.com article uses a link to [1] as evidence for the "electric brake system", but this is the _parking_ brake (which is indeed an electric motor, but is an entirely different system, separate caliper, etc). The parking brake will remain engaged even if you lose 12V, so you won't roll away if power cuts out (which you'll know if you've ever tried to tow a Tesla that went totally dead while parked). An electronic park brake is a setup seen in many modern cars.
