After infected by rabies, during incubation period but prior to brain being infected, having rabies vaccine can help the patient survive?

Yes: A person infected with rabies will not show ill signs at first. If he doesn't get rabies shots, the virus will travel to his brain. The incubation period from the time of infection until the signs and symptoms show up, is variable (about 3 weeks to 3 months). The last chance to get rabies shots and not die, is uncertain but is some time before any symptoms appear.