I believe that if Yar had lived, Worf would keep being portrayed as the dumb Klingon who wanted to kill Troi's baby, who wanted to Blow a hole in the viewscreen, who keeps reminding people I AM A KLINGON, That "THERES ONLY ONE BRIDGE, ONE RIKER, ONE BRIDGE", and probably would have been shown growling at the borg from his sensor station. Worf didn't really get any respect til later TNG.
I did love Yar's character, and I wish she had not been killed off. I dont think Marina Sirtis would have left. Afterall, she didn't leave when Whoopi kinda stole her job.