I am not any type of expert with GSD's but I can say one thing and one thing only about those last days. Growing up we had a female GSD that survived 3 strokes and spent every single day up until her last out in the yard playing with us kids at her ripe age of 18 years old. My mom never discouraged us from playing with her because Cheyenne lived such a full and happy life doing what she loved up until the end. Of course I'm not saying anything was ever done knowing it would cause her pain and/or discomfort so please don't read this that way. All I'm saying in my humble opinion is that you could just find something that your dog loves doing and just do that. Your dog will love their life as long as it involves you.
Hail Gunther 7-2-2013
If at first you don't succeed, destroy all evidence that you ever tried.
"Some people never end up going crazy...what a truly terrible life they must lead." - Unknown