Fact is you couldn't ride a limp horse, even now days injured horses, and I'm talking about the injuries we'd see on the horses in game, would most definately be put to sleep. Which is perhaps why limp horses should be done away with all together.
But playing some more this evening, and buying a very expensive horse and having it get injured after just two battles I would like to suggest making our horses a little more sturdy, yes it's already unrealistic, a horse taking more than one blow with a sword is amazing but this is a game after all, I really dont see what limp horses offer to the game... More immersions? No because no one could or would ride an injured horse.