Will God hold a Muslim accountable for injustice and betrayal in matters between him and his Lord, or will He forgive his sin simply by the wronged person forgiving him after his death? And is absolving the deceased's financial obligations the solution to getting rid of the sin?

For repentance from a sin related to the rights of people, four conditions are required: remorse, cessation, determination not to return to it, and restitution of rights to their owners. If only the rights are restituted without fulfilling the other conditions, then the repentance is not accepted, and the sin remains. If the owner of the right forgives, or the heirs return the rights, the right to demand recompense on the Day of Judgment is dropped. However, the sin itself is not effaced due to the incomplete fulfillment of the conditions of repentance, and its matter remains subject to the will of Allah Almighty, as confirmed by His saying: "Indeed, Allah does not forgive association with Him, but He forgives what is less than that for whom He wills."