Will Allah forgive a committed person who went to a sorcerer once in a moment of weakness, and then died a short while later? And how can his daughter atone for this sin on his behalf?

If a person repents of their sin, Allah accepts their repentance and pardons them, for Allah Almighty says: "And it is He who accepts repentance from His servants and pardons sins," and for the saying of the Prophet, peace and blessings be upon him: "The one who repents from sin is like one who has no sin." If they do not repent, then their matter is with Allah, and it is encouraged to seek forgiveness, supplicate for them, and give charity on their behalf.