Horses are abandoned to die in CO all the time. My friend got the same call that Colorado Horse Rescue got about a horse down in the snow. But since none of the other rescues in the area would go they went with 4 wheelers and made a sled for the horse and pulled it out to haul it home. They set up a hoist and sling in their living room and the vet encouraged them to keep trying because this horse had a strong will to live. I don't know how it survived but it's doing ok, not going to be pretty though. He had severe frostbite and lost his lips and more. They were just afraid he would founder. So far so good, Miracle is a miracle but I think they changed his name to Livingston after his time in the Livingroom. He had been a calm horse there and may be an unadoptable horse but he will live out his life at their place as long as he is able to live well enough.
Apparently the hunting parties abandon horses regularly when the weather turns suddenly.