Are punishments like Hudud in Islam and man-made laws imposed for deterrence and intimidation only, or also for reform? And how can there be reform for someone who has been executed?

Punishments such as hudud (prescribed penalties) and ta'zir (discretionary punishments) in Islam were legislated to deter and prevent transgressions. They deter the ignorant out of fear of the pain of punishment and the disgrace of public humiliation, thus safeguarding the lives, security, honors, and properties of societies. If the perpetrator of a crime is certain of accountability for it, they will cease committing it, which leads to the establishment of security and tranquility. Allah Almighty says: "And there is for you in legal retribution [saving of] life, O you [people] of understanding."