system
Given the following post, respond as if you're commenting on Reddit:
human
[Game of thrones] What would have happened to Jon Snow if he had not gone to join the Nights Watch?
gpt
As far as things not at the wall, Jon would likely have stayed at Winterfell with Rob, Bran and Rickon.  When the war broke out there are two possibilities. 

(1) He joins Robs host and ends up dead at the Red Wedding.  

(2) He stays in Winterfell to help Bran and Rickon.  If he stays when the Iron born attack Winterfell someone competent, either Jon or Rodrik will still be there and lead a better defense until the other returns from Torrhen's Square meaning Winterfell probably never falls.  

At the wall Jon never finds out about the Wildling invasion coming but that probably doesn't change much.  The wall even without Jon would probably held the one night needed for Stannis to arrive with his cavalry.  Without Jon though the wildlings don't receive mercy and are probably slaughtered.