Thankfully, Monolith is thinking further and allowing fans of the end-game to slaughter Orcs indefinitely with the upcoming free Infinite Shadow Wars DLC.
Expect Infinite Shadow Wars to arrive when the first Orc tribe DLC releases.
The only difference in Infinite Shadow Wars is that the battle will go on continuously as you fight Orc after Orc to defend your property.
Confirmed in a recent livestream, the developer noted that Infinite Shadow Wars will be a free download.