well, 5 yrs is 5 yrs.
my husband's father got diagnosed with mulitple cancers & sent home to die. (it was too progressed for treatment)
one horribly agonizing month later, he was gone.
be supportive & help your dad keep a positive outlook! don't let him take the odds & percentages as a cold hard death sentence. don't you think that way either. the power of the mind is great.
enjoy as much time with him as possible so you'll have no regrets ever.