I went through the same thing with my Great Dane. I never got to take him on one last rabbit hunt because his hips gave out too quickly. I was stressing about when to put him down because his personality and love was still there, but he ended up passing in his sleep. He was an amazing dog, best friend, travelling companion and hunting buddy there was. I got 10 1/2 amazing years with him, which was way over what he was supposed to live according to the vet.
Thats really old for a dane, isn't the average only like 7 years?