So I just finished the game a few moments ago, and now I'm a tad confused. I killed shit head and the late title card and credits went through and then I loaded back in the game. I just wanted to make sure that the only thing left to do is the side quests now right? There is no real story or prologue to find with certain characters that John had a lot of contact with, it's just to top off any side quests and to run around the world if you like. 
 
I'm just wondering because I have no interest in doing the side quests, and like many I find the kid annoying to play as, but if there is some kind of prologue I would be willing to ride around a bit more to find it.

There are no story missions after you killed the guy who killed John, at least as far as i know. 
 
And yes, the son Jack is a pain in the ass to play as. He was the only reason I didn't wander around in the game world after the main mission.