you are going through one of the worst things you will ver have to deal with, there is a conflict going on inside you. if you go spend time with your father you will see just how ill he is, and concrete your thoughts about his dying soon, however if you stay away and something does happen to him, you will be riddled with guilt. by staying away you can remember your father as the man he was rather than the man he is at present, by going to see him you are preventing the guilt. this is one decision only you can make as only you know how you want to remember your father and how well you will cope with the guilt if you choose not to see him.
either way, a compromise could be regular phone calls, even if he can only whisper, he can still listen to you. listening to a loved one talking about general life things (e.g something on the news or what they have done that day) gives the ill person something to think about other than the situation they are stuck in, and i am sure the best medicine for anyone is to hear that someone loves them.
go on pick up that phone and chat away x