What should one do who has sinned against another financially and repented to Allah, but is unable to face the person or return the money due to incapacity, and fears meeting Allah with unaddressed grievances?

If an wronged man has a financial right [owed to him], it must be returned to him if he is alive and his whereabouts are known. One's obligation is not absolved by performing Umrah or anything else. If he dies, the right is to be given to his heirs. If they cannot be found, or he died and his heirs were not found, then the money should be given as charity on his behalf. If you do not possess the money to fulfill it, it remains a debt upon you until you pay it. And if you die before fulfilling it, and your intention was sincere, then Allah will fulfill it on your behalf.