Remember the good times mate, you were lucky to have him. My father died when I was 13, my wife the same, fatherless at 13. We never had a father to guide us through our teenage years, help us make those important decisions in our 20's...and our children never had a grandfather. We never had to argue and defend our decisions - we were lost, fathers are so important.
I don't know if it's tougher losing someone suddenly, or a long illness. My mother died from pancreatic cancer 9 years ago, 10 months watching her fade away. The trauma of the death sentence in the first few days, and by the end it's just a release, all our goodbyes said, some skeletons out of the closet, and being told where to look for the hidden ones she didn't want to confront.
Tell your kids about him, they need to know what Grandad was like when he was your father.