
Ours lived until about 12ish but others longer. My brothers boy (unfortunately my brother died when King was only a year old) died just before his ninth birthday with cancer. He was the most wonderful, most handsome Rough Collie and it was such an awful way to go, but he was put to sleep within 3 weeks of his symptoms showing. It was awful to see a big solid dog turn into a skeleton in such a short time.
I have a dog who's nearly 12 and I know your worries but as the other poster says whilst they are happy and still going strong don't even think about it, what will be will be.