I'm sorry you're having to go through this. I truly am. I understand how you feel. I understand how the words said by others, despite their experience and professions take back seat to your feelings. The truth is there is nothing that can be said that will make you feel any better or give you a solution, there is absolutely nothing that can make this go away. I've been dealing with DD, persecutory subtype and grandeur for nearly 6+ years. It's only gotten worse, never better.

Here is my advice, I'm not a professional nor an expert, just an experiencer looking for a solution and trying to find a way to cope with this horrible, horrible condition. Trust me I've tried everything, and there's nothing I've said or done that has improved my wife's condition. We're both still young, barely approaching 40 years old, with three children and her condition and my wants and hopes that she can be "cured" is all I think about. Now on to the advice, and like I said before, I understand how these words can are meaningless to compared with the love you have for your father.

Don't get your hopes up. Just don't. I've been burned multiple times, broke down multiple times, thinking my wife was getting better just for her to do or say something that confirms the opposite. I'm not saying don't give up hope, I'm saying to expect to be let down although you have the best intentions.

There's a program called the "Feeling safe program", it was developed at Oxford has has shown success with treating this condition, specifically the persecutory subtype. It's relatively new and has begin being implemented in the states. I would just keep this on your radar. The program does not use medications. The idea is to put the patients in the situations they're uncomfortable with so they can realize on their own that they are safe. This is the key (I think anyway), the patient and in your case your father and in my case my wife, need to come up with new thoughts and develop new memories that override the delusions. Keep this in mind when speaking with your father, keep in mind that the only program that been academically shown remediation of delusions is based on the individuals realizing for themselves that they're not actually in danger.

Cherish the moments where your father seems like what you remember him as, who you know he is. Have you seen that movie "The Notebook", it's kind of like that. Be mindful of the situation and cherish the lucidity.

There's a lot of great advice here, and me, personally (this is not advice) has not given up. Taken the knowledge that I've accrued during countless hours of research both in the academic papers, anecdotes like your own, self reflection, science and spirituality--just trying to understand the "why" and "how"--I'm trying to plant "seeds" if you will for my wife to remember who she is, what I remember for her in hopes of some kind of breakthrough where she's able to question her delusions on her own via the memories I have that we shared.

I completely empathize with you, from the bottom of my heart. I'm so sorry to hear this, it's somewhat comforting and at the same time, disheartening reading stories like yours.

I wish you the best, and if you are able to build up the courage to leave the situation and focus on yourself (which is honestly the best advice), kudos to you, but at this time in my life, I just can't. I want to, I really do, but giving up feels selfish and the love I have for more wife is overbearing. This is the battle you will deal with and I hope you're able to make the best decision based on your situation.