Not quite 100%. The Milwaukee protocol has shown some success in treating symptomatic rabies infection. A few dozen people have survived rabies.
It doesn't work all the time, but if I were bit and started to show symptoms, I'd give it a go!
It has saved a handful of symptomatic rabies patients. Most patients who were treated with this protocol died anyway.
According to this (non-medical) website, only 29 people have ever survived symptomatic rabies, and most of those survivors had some sort of pre- or postexposure prophylaxis.
How Many People Have Survived Rabies? Every year, approximately 59,000 people worldwide die from rabies. Vital Signs: Trends in Human Rabies Deaths and Exposures — United States, 1938–2018.
The chance of survival of symptomatic rabies is so low that I would not casually refuse prophylaxis in case of exposure in the confidence that I can be cured if I show symptoms. There is a reason rabies is so feared and there are multiple efforts to control rabies.
One of my friends actually was personally involved in the handling of a fatal human rabies case. There was a paper published on it.