I'm sorry to hear that, someone I knew closely died of pancreatic cancer and died 6 weeks after diagnosis which is why it scares me so much. Did your grandfather smoke, or drink a lot of alcohol? Or drink a lot of tea or coffee?
He lived about a year after his diagnosis, which occurred when he was jaundice. His health / quality of life was ok after, some weeks were good, some were bad, but yeah it was stage 4 when they caught it, and there is / was only so much you can do, especially 23 years ago.
Fun Fact: He worked on the Univac! Spent his career with Unisys afterward.