I used to have this problem with caravans, where spawning monster would stroll out and kill my caravans. However, I soon realized that is was due to the fact that I was sending caravans on incredibly long journeys into unprotected lands. Mainly, this was a lack of oversight on my part and after a couple of times of this happening, I started picking safer routes and sending troops to nearby forests to watch for pesky spawns. I think alot of people are spreading their kingdoms very wide and hoping that a single caravan can traverse the great distances without fear. To allow caravans to respawn or some how become invulnerable to attack would make them way OP and make have a significant effect on the player when trying to take out a rivals trade network. I think that being able to add guard attachments to caravans is a decent idea, though I think significant limitations would be required to prevent caravan guard units from becoming super armies themselves.
