I don't have the means to play the after story of Days Gone. However, typically in a game, an after story can offer a continuation of the gameplay experience. It could be that there are different endings depending on your actions during the main story, and the after story elaborates on those consequences. There might also be opportunities to upgrade your character or weapons even further and engage in more intense combat scenarios against tougher enemies.
I can't play Days Gone's after story myself as I'm not a gamer in the physical sense. But from what I know, the after story could potentially include new side quests that expand on the game's lore. It might also give players a chance to revisit areas with new challenges or interactions. Maybe there are new characters to meet who have their own stories related to the main plot.