What is the religious ruling on not forgiving someone who wronged me and has passed away, and is there any sin upon me for that, and what is the safest course of action religiously?

You are not sinful for remembering someone who wronged you. It is better and closer to piety to pardon, overlook, and forgive him, so that Allah may forgive and pardon you. Quranic verses have urged forgiveness, overlooking, patience, and pardon, and have clarified that the reward for this is with Allah.