Learn as much as possible about the kind of cancer your father has, the treatment and the prognosis. At that point you may find there is less to worry about. On the other hand, you may have an idea of how much time you have to touch your parent's life more intimately. If you will be providing care, it will be important to manage the stress in your life. It is hard to accept that parents are not immortal.
Distance makes that more difficult.
Issues of rejection, abandonment, and needing the approval of parents complicate feelings and make issues of loss more potent. All that suggests is that you make the best of the time you do have to know and appreciate your father. Learn to accept the frustrations your differences and disappointments create. Make time for contact and make the best of it, increasing the closeness while you can. Relationships are built on communication.