Unfortunately, it would have been impossible. A horse must have 4 legs. Because of the distribution of weight on a horse's legs, even one leg being sore can be a death sentence (now sore is treatable, but if a leg is broken, he's better off dead). If the weight meant to be taken by the forth leg is evenly put on the rest, they will break under the pressure (horses can stand on three legs, but if they have to move, their legs will most likely break. That is why a common treatment for a horse with a bruised leg is to keep him as still as possible until it heals, before he is able to damage it more by walking on it). There was only one case of a horse with a prosthetic leg who lived a healthy life (he could not run, or be ridden, or do anything that makes horses happy, but he was alive).
Thanks, I was actually wondering about that, given that there are videos of dogs walking on hind legs without any problem.
Poor horse.