The worst thing a dying man can get is pity, honor his wish for the most part, but have a chat with him as well. I'd tell him that I'd treat him normally, but do remember that he is your father, and it's only human and natural to be hit hard by the news. As your father, he does still have a responsibility to understand and sympathize with how your family is feeling, even if he is man that'd prefer not to be pitied. There's always a butter-zone between pitying him too much, and letting him slip away as if nothing happened, both ends being a terrible result. Talk with him, and find a combination between treating him like a normal person, but also accepting the gravity of the situation.
All the best, Aborted.