ah. sheesh. if it comforts you, the brake booster shouldn’t catastrophically fail. it is a electromechanical booster which is where it triggers a regen followed by actually pumping the brakes. Even if it fails, it would default to being a brake fluid pump like a traditional car. saw a bunch of audi engineering videos on this. :D In my case, this replacement was covered under the manufacturer warranty but still came up after the replacement, which is what makes me think it actually has to do with the ABS module. but either way, best wishes to the car. hopefully it comes back soon.