I did what I thought was a completion of my trauma work, 15 years ago (5 years of therapy). I actually didn't start having nightmares until I was a ways into therapy, and they stopped somewhere before the end of it. I occasionally have dreams now with some kind of more creepy content, but no nightmares.

I'm sure you know, they are a symptom of PTSD. Although I find some of the other symptoms of PTSD flare for me from time to time (especially flashbacks), they haven't come back for me.