Is the repentance of one who has repeatedly committed a major sin, the ruling for which is execution, accepted, and does Hajj nullify this major sin?

Boldness in committing sins is a serious matter, and sincere repentance is obligatory. The repetition of a sin does not prevent the acceptance of repentance if the servant is truthful in it. If the sin relates to the right of Allah, then repentance and concealing oneself are sufficient, such as adultery for a married person. However, if the sin relates to the rights of created beings, like retaliation (qisas), then the guardians of the blood must be empowered over the person, and they choose between qisas, forgiveness, or diyah (blood money), knowing that the establishment of hudud (prescribed penalties) is the responsibility of the ruler.