There is no sin in our religion from which people cannot repent or which Allah refuses to forgive. Even though the person had committed fornication, had murdered or had joined others with Allah. Every type of sin is subject to repentance. The Glorified Allah commands:
“…Except for those who repent and reform themselves. Because Allah is The Forgiver and The Merciful.” (An-Noor/ The Light 24:5)
“And those who do not call for help with Allah another deity or kill the soul which Allah has forbidden [to be killed], except by right, and do not commit unlawful sexual intercourse (zina). And whoever should do that will have sinned. Multiplied for him is the punishment on the Day of Rising, and he will abide therein humiliated; except for those who repent, believe and do righteous work. For them Allah will replace their evil deeds with good. And ever is Allah The Forgiver and The Merciful. And he who repents and does righteousness does indeed turn to Allah with accepted repentance.” (Al-Furqan/The Criterion 25:68-71)
Hudud punishments have no relation with repentance. They are related with the worldly life. If the person is proven guilty of the offense and the required conditions about the offense are met, punishment is given although the person had repented. Every hudud punishment and its conditions must be investigated one by one.