I read on a guide for chief bandit that you can solo headless horseman lvl 70 with meso explosion But the purple ghost mobs 1 hits you so how Are you supposed to juke them while you kill him?
I would say look for a different map that has headless horseman but no elder wraiths. And put a point into meso guard at lvl 71, it should help you survive.
The area boss respawns several hours after it's been last killed by a player, I don't remember what the respawn timer for Headless Horseman is though. He does spawn on multiple maps in that area.