Thanks again to all of you for your support. We had Zealynd put to sleep today, and while it was hard, it was not as awful as I had feared. Of course, this was not my dog, but it was very emotional for me anyways. It was very peaceful, he died with his head in his owner's lap, and my friend came away knowing that she had done the right thing.
I can see him now, chasing all the cats at Rainbow Bridge.