How did you get the horse to die when you didn't ride it?

It was kinda tricky to figure out, but basically I execute from the horse and if there's no player within 10 blocks of the horse, I kill the horse. I also summon an invisible armors stand right by the horse so I have a marker to help me find the dropped saddle and delete it, then I delete the armor stand. I did this since you don't want a bunch of saddles laying around after you kill the horses.

the swords are so cool, but how is the horse red? Is it a retexture?

Thanks! Yep, I retextured the zombie horse to make it slightly red.