It all depends what person your father is to you if you care about him stay strong with it but this is a bad thing I've got to tell
Your father will die soon there is no rescue unless you get back his will to live there is absolutely no thing that shall keep him alive I do not wish to say much either and I understand your frustration (I lost my dad at my age of 10)
He must have had a hard life but he must also have done things wrong which he rgrets it all comes back to you in the end and he has lost his will to live I am sorry for saying this but be prepared for pain
Yet be happy he lived so long and that you have a dad at your age mine had 56 when he died
You see there is still hope that he will live yet I dare not say the probabilities
But do not take all discourage in what I say I am a lot younger then you think fysically I am not yet an adult I might be wrong but the chances for that are minimal
Be strong help your father all you can if you love him, you do not have to give everything up since you only can take off 4 days a year
But your dad must have the will to live I know your mother wants to support him but I don't think she is ready for his death he can die anytime but there is still hope so do not give up the thing you must concentrate on is his will to live his fysical health is the doctors job