Post exposure prophylaxis is almost 100% effective (see WHO position paper: https://www.who.int/publications/i/item/who-wer9316). It takes advantage of the relatively long latency period of the virus (usually weeks/months, but in rare cases years), so when administered before symptoms show, it is almost always effective. In this case, the virus is gone and there is no risk of it re-emerging.

This doesn't mean you can't get rabies again if reinfected. As another post mentioned, the rabies vaccine is usually topped up with a booster (frequency depends on risk areas). Post exposure treatment is always recommended regardless of whether a person is vaccinated or not.