My father suffered from dementia during the last 15 years of his life, with the diagnosis of Alzhemer's. And I can say that that experience changed me, and not for the worse. And I can say, my friend @janaveda that that experience changed me, and not for the worse.
It gave me the opportunity to be able to give back all the love he gave me. It gave me the opportunity to be a better person. When he left, it was not only shattering, but it also helped me learn to differentiate the important things in life from the accessory things.
It is good to know that something in essence harmful did you good through caring for your father. Although they depart on this plane, their love accompanies us all our lives.