This is true, she will simply develop more toxic ways of manipulating that are hurtful. But, Dad is reaching out for guidance both here and with a therapist, so he has a better chance of learning important things so if he does end up with his marriage ending, he will be able to say he tried, and he will also be able to walk away knowing he is making the right choice. Also, when it comes to finding a new partner in his future he will be able to recognize some red flags so that he doesn't end up in another relationship that is unhealthy.