It all depends on how bad it is.
Horses are very different to Humans, although there are similarities.
A horse have slightly more than 200 bones all together.
80 of these are actually in their legs. A quite amazing number.
It would of course depend where the horse break its leg or even if more than one leg is broken.
The chances of an acceptable recovery are (due to the vast number of bones in their legs) unfortunately very slim.
In most cases, a broken leg is slowly but surely leading to the final outcome of death.
There have been some recoveries but they are far between.
Horses in the wild stand no chance with a broken leg. They will easily be hunted down by predators. Even if no predators are present, they will most likely get severe infections and succumb to diseases or infections thereof.
If your horse break one leg, then it might have a slim chance but more than one gives almost always a final outcome.
A veterinary will be able to advice further.