How horses break our hearts...
So sorry about your horse! Our first foal broke his leg out in a flat grass pasture with his mother. He had 3 surgeries then had to be put down. We have had a number of young horses who needed prolonged stall rest.
*We had a horse here who belonged to a friend who was an enormous yearling warmblood and developed severe OCD lesions. He was predicted to never be sound. After 2 surgeries and over a YEAR stall rest, he is 100% fine with resolution of his lesions and is coming 3 now.
*We had one of my FAVORITE yearlings out of my beloved CCI** OTTB mare get kicked in pasture and break his hip. The break "slipped," and we were advised to put him down. That was over a year ago, and he is coming 3 this year. He is perfectly comfortable, and a favorite. He has gotten gradually better although I do not think he will likely ever be rideable.
*One of our nicest fillies was stepped on by her mother and injured her right hind. She had surgery which did not fix the problem, but she has had excellent care by our phenomenal vet and farrier and is sound and comfortable. She won't hold up to competition as she still has some deformity of that leg, but she is lovely and her breeding is lovely so will likely breed her. Of course, she has amazing gaits, so every time I see her trotting in the pasture, I want to cry....
Horse number one lived in a stall. We rotated horses (usually our horses live out) so he always had another horse he could see across the aisle. He hated it, but we all survived somehow. For our second horse, we ended up building a stall size paddock next to the other horses. He spun donuts all day inside the stall so we figured it was less stress for his hip to be outside in a confined area where he was less agitated. The third filly had to spend a couple months confined. We used a stall and a stall sized paddock and put she and her Mom in and out. I think it really depends on the individual horse. Some horses tolerate stall rest pretty well with a jolly ball and some toys, and some go bonkers.
I have been considering my alternatives - happy life in the pasture albeit neurologic, paddock only but still separated from the horses or round-pen restricted but adjoining the other pastures (and thus leaving the possibility of neck-wrestling and further injury still open).
I can 100% understand why people put horses down if they will not be useful in their program because, god knows, they are so damn expensive. We, however, like you, just cannot do it unless the horse is miserable or in pain. Fortunately, the injured ones always seem to find someplace they are useful in the program, as babysitters for the youngsters if nothing else. My old NZ TB who developed something neurological as a fairly young horse when he was going prelim, has turned out to be a fabulous babysitter, and he has always been a big pet! So you never know.....
Let me just point out that I do not expect for Cary to ever be a normal riding horse. In fact, I doubt I will ever be able to ride him at all. I am okay with that. I know this too would not make a lot of sense for a lot of horse owners but I have come to terms with him always being just a companion animal and I am okay with that.