In Chapter 16 or "Notes" from The Things They Carried, has the narrator successfully transitioned from Vietnam to civilian life?
Yes and no. Even though these stories are "fictional," all readers of The Things They Carry realize that Tim O'Brien, a Vietnam Veteran, includes more fact and reality than fiction; so if one thinks of O'Brien as the narrator, the answer is that yes he does transition, but also "no," because no one can truly leave behind a traumatic experience like combat.
The narrator, after relaying Norman Bowker's heart-rending experience after coming home from the war, discusses his own "transition" into civilian life. He believes that because he was able to go to graduate school right after the war and become a successful writer that he has successfully transitioned. Similarly, he did not experience the night sweats and flashbacks that so many of his comrads in arms did, and if one compares his post-war life to Norman's shiftless, painful post-war experience, then it is easy to argue that O'Brien did transition quite successfully.
However, when O'Brien reads Norman's letter, he is impelled to write a short story about Norman, and the experience brings back his bitterness, confusion, and discontent--all regarding his combat experience. Writing for him is cathartic, but it also forces him to realize that he rarely speaks about his war experience.
On a personal note, O'Brien--though it seems that he has maintained a victory of sorts over PTSD and depression--realistically portrays the struggle that so many veterans, including those returning from Iraq and Afghanistan today, experience when they try to assimilate back home after combat service. My husband has been to Iraq twice, and when he read O'Brien's description of Norman Bowker, he told me that it was exactly how he felt after his first combat deployment.