I wish I could offer advice, but I am also very recently estranged from my family. I really have no idea what I will do when faced with their health issues.
As for making the pledge, I don't want to come across as harsh Cant, but I do feel like this is something for you and not for your father. It will make you feel better. I would say this even if your were making a contribution to charity in his name. It may help your conscience, but how will it make him feel? Will he understand it? I don't know enough about your relationship to answer that, of course.
I've been praying for guidance with my own estrangement, I'll add you to my prayers