I'm not trying to sound cynical or anything but will not going save him? You could go and if, God forbid, he passes... Leave immediately and go home. Second, if you don't go and (as we all hope) he doesn't die, it was a waste not to go.
I live 5 hours from my hometown. I got "the call" that he was doing bad at 7:00 am. I called off and before I could even get on the highway, I got the second call... "don't rush" :(
I know it's a tough decision but what would HE (grandpa) want you to do?
Good luck in your decision and I'm sorry for your situation. I was VERY close with my grandfather and miss him dearly!