Who would win.

The Headless Horsemen

or

The Horseless Headless Horsemann. 

My Opinion: The Headless Horsemen wins cause it's shown in TF2 Holloween event that horseless headless Horsemann can be destroyed but with a lot of force and power and, i believe the Headless Horsemen can defeat him but it would be endless until The HEadless Horsemen wins by Either Decapitation or fighting from a far distance and it's never shown that the Headless Horseless Horsemann is immune to Decapitation so it's possible for the headless horsemen to win that way