If you are certain that a person is a psychopath… scientist say that psychopaths can’t be changed. That their brain is wired in a different way.
If they are abusive, it is a common mistake for people to stay with their abusive spouses in hopes that they will change their ways.
Psychopathy, along with BPD and malignant narcissism, is an incurable personality disorder. I wouldn’t bank on the person changing suddenly by some miraculous epiphany.