I believe you can get a horses spirit back. I've taken in horses that have been beaten and neglected. They had no personality, no play, no zest for life. It comes back. Sometimes it takes years, sometimes weeks, but you can get it back, with patience, time, love, and understanding.
Back in the "cowboy days" they used to "break" horses. Now most people train them. There is a difference. A horse can be well behaved, have excellent ground manners, and even work like a "machine" and still not be broken. IF it is trained properly. It usually takes a lot of time and sweat to get them that way and that is why some people will opt to "break their spirit". You can bring your horse back though. Good luck.