Quality of life issues

Scooby in better days--a beautiful and sweet dog

My twelve-year-old Aussie had been gradually improving since his latest attack of idiopathic vestibular disease. The high point came maybe last Tuesday when he went down the stairs to the backyard (two steps) by himself without falling. He's been walking to and from his bed without falling on my hardwood floors. I cheered and called the vet, who also cheered. But the last couple of days, all the progress has slowly faded away, and this morning he wouldn't get up--I lifted his hind quarters, but he fell three times between his bed and the bedroom door. I finally got him outside, using a towel for a sling to hold up his back end and, yes, he fell down those steps. I stopped by the vet's on my way home from the grocery, and Dr. John Minnerly (my new hero at University Animal Hospital) said he did not like the news at all.
A little after noon, I brought Sophie in and called to Scooby to come get his food. He didn't come, so after a long while, I went out to his dog house and banged on it. All I could see was his back end. I got down and crawled onto the porch of the doghouse to look inside. He lay on his side, panting heavily, and resisted all my pleas to come out, so I tried dragging the back legs. Didn't work. So I crawled in and got his collar and pulled him out. He offered to bite me--Scooby would never really bite, but he'll put his teeth aroiund my wrist to say, "Stop what you're doing." I had to pull him out twice before he finally came out, stood up, and staggered over to his food--which he ate all of. By the time I went inside with Sophie, my heart was beating like a trip-hammer. Called the vet, who also panicked, and said he'd be right over. Long story short, he and his technician decided--and I heartily agree--that Scooby would be better off in their clinic over the weekend. I don't want him to have a catastrophe while the vet is closed, so that I have to go to the ER Clinic. And Dr. Minnerly and his staff know and love Scooby. They'll watch him and monitor his condition.
I have really mixed feelings here. The last thing I said to Dr. Minerly was, "Think about quality of life issues." How miserable is Scooby, trembling every time he tries to go up or down stairs, safe only in his doghouse or his bed, afraid of falling all the time? Christian asked me that tonight, and I said, "He's so scared. But what is he scared about? Pain? Death? We're all scared about those." I have no idea how to help Scooby best. He's been the most loving, wonderful dog I've ever had but now it's like I can't reach him. He reminds me of an old man who's had a stroke--probably doesn't see or hear well, his back legs don't work, and he gets confused. And yet he enjoys love and attention--and his food--and he makes weak attempts to play with Sophie.
Sophie is a bit devastated. She doesn't understand why she was outside alone for two hours tonight while I went to dinner. She misses him.
What a mess. Excuse me while I reach for another Kleenex.