The only way I see a plotline of Vader trying to destroy the Empire from within working is if he’s doing it for selfish Sithy reasons, wanting to take Palpatine’s place and continue the whole “rule the galaxy as father and son” thing. Vader is not the kind of person to admit that he’s wrong, he’s the type to double down based on his emotions. Because he can’t let go of anything. Through the whole movie he keeps avoiding the truth and refusing to admit to his feelings. “If that is your destiny.” “There is no conflict.” “If you do not fight, then you will meet your destiny.”
The guy’s been at this “right hand of the Emperor” business for over 2 decades. He had multiple opportunities to do the right thing but refused because he couldn’t let go of his hatred and pain. It would take something enormous to get him to even think about changing his mind, like his son being electrocuted to death right in front of him.