Ned's survival could've worked out a whole lot better or a whole lot worse for Sansa Stark. Ned's 'traitor' status broke her betrothal to Joffrey, and that may have still remained the case, but there's also a chance that Cersei would've followed through with the marriage. The two routes would've been: A) Sansa married Joff, Cersei wouldn't get the military might of the Tyrells, but she would get a tighter grip on the North, despite a probable attempt to steal Sansa back. B) Sansa's betrothal was ended, but she would remain in King's Landing to keep ties with the North without making her Queen.