If he wants to leave, but is still hanging on, it's important that you just be with him, to listen and touch as possible. There may be something he hasn't said yet, or someone he still wants to say "goodbye" to. If you are there listening, you may be able to help him in some way. But as for prayers, why not just say a loving prayer, for your dad's highest good (not in your opinion, but whatever his soul says it is). I know it is painful to see him in this situation, but dealing with it may be part of YOUR lessons, who knows?
Love and hugs to you all.
Had done that... Listening and touching... My father had not been able to say good bye to my sister, there had been moments in which they had been alone but, my dad has not touched the subject.... On one occasion, I was with him and he started to say something to me - for me to tell my sister - like a farewell... I told him to stop, that I'd better recorded it.... I haven't shown my sister the video, hoping he will tell her in person, had not had happend, though .. He mentione other relatives, I recorded several videos, I haven't shown them either.
We - as family - had not raised the alarms yet to other family members because nothing is for sure... But my father - had told his brother, or a cousin came to visit last week and she had saw how deteriorated my father had become, she came last November and since then, the difference is pretty obvious.
There is an issue here, my mother and I had awcknowledge the fact that he wants to go, my sister and brother do not... We both had agreed that perhaps they are in denial... After reading your post... I, my self began to doubt, perhaps I misinterpreted the signs... But after more experiences-details, phrase he had said, I think is more that I do not want him to die, every day is an oportunity to be with him...
A while ago, when I was near his bedroom, I heard him telling my mother that he was leaving and that he wanted to pray, I went into the bedroom, he was lying on his side, I hugged him and took his hand... And, while my mum was praying I was thinking about just what you mentioned, talking to his higher self, whatever he decides... and he closed his eyes to rest, not to die.... I also observed that he was still breathing.
When it is my turn to stay with him at night, I hold his hand... as I have done with babies, with my nephew, when they are loose, not clenched or fisted, a sign that they are resting or sleeping deeply... I have noticed some communication with the hands, pats or squeezes....
When the hand goes away, I become alert.... What he can't do in the day, he does at night.... He takes out his portable urinary catheter... and won't let me put it back in, he pulls down his nappies - they're the pants type.... It's not convenient because then he wets the bed and we've already had to clean him up, change his clothes, change the sheets at 3 am.... I think that, as he has always been very polite and had shown good manners, at night he indulges himself, much to my dismay, to do what he wants and be more comfortable.
Usually there are 3 of us in the bedroom at night, my mum and dad in their bed and, another person in an armchair, he had the urge sometimes to get up, he doesn't have much strength and can go and hit the floor.
I had been learning about the touching part, I am not used to it, I am giving my self that oportunity - if I can say it that way.
Do you know a loving prayer? I will want to pray it for him... I tend to be rather abstract and very concise... When I thought of his higher self, I think it just like this : "be it done what thou wilt"... I would like to offer him something more... elaborated?
Know that you can also talk to him if you feel the need to or if you have something to say, and if you'd like to write a letter to him, 
