If your horse dies and you want to revive it, travel to the following location in the far south of Hyrule. Continue south past Lake Hylia and southeast of Faron Grasslands. It is southeast of the Highland Stable. Cross the Horse God Bridge to see something that looks like the fairy fountains. Interact with it and pay 1,000 rupees to summon the Horse God to revive your horse. Whenever one of your horses die, return to this place to have them revived.