Fours years ago I too had a type 3 shoulder separation, I did not have surgery and recovered fully with no complications. I cannot speak to the value of surgery but not having gone through with the procedure has not limited my swimming. I too swim competitively putting in typically 750K meters a year and in the 4 years since my injury have gotten increaslingly faster. My only downside is that I have a very strange bump on my shoulder.
My recommendations are that if you do not choose surgery find a good physical therapist and do everything they tell you to do. Take time rehabbing, run + bike (on a trainer) more while the shoulder heals. I was back in the water 2 months after the injury doing very easy workouts.