Hey, Stanlos!
Diana's mission of peace seemed to pretty much end at the end of the Rucka run, which saw Paradise Island ravaged by OMACS, Diana having lost the world's trust after killing Max Lord, and the Themiscyran Embassy being closed down. Nevertheless, it could still be assumed that Diana wanted to continue on her mission after that.
It was really the New 52 where that mission was completely jettisoned. In none of the books in which Diana appears has she ever said a word about being on a mission of peace. It's just not something New 52 Wonder Woman seems to be even interested in pursuing.
Brian Azzarello established in his Wonder Woman run that Diana rescued Steve Trevor from her sisters and saw him as her "ticket" (her exact words) off the island so she could go out and explore the world (and get away from her "sisters," who were treating her like crap.) She volunteered to take Steve home, and then made very little effort to visit home once she left. From there, she's pretty much just been interested in being a more generic superhero: beating up the bad guys and little else. She's also been written as having severe rage issues, which make her much more violent and willing to kill than any other member of the League.
She has been starting to improve in the comics. Geoff Johns has just mysteriously decided to start writing up her compassionate and peaceful side after three years of writing her as little more than a bloodthirsty barbarian. In the Finch Wonder Woman run, she's experiencing moments of extreme violent behavior, but the last issue saw her question why she's acting this way, so it's probably going to be revealed that something is affecting her to make her act like that.
But still, no. She has not in any way stated that she's on any kind of a mission to bring peace to the world or anything else. The New 52 has made her much more like Xena or Red Sonja than Wonder Woman. Things may be about to change, but that's the story thus far.
Though much is taken, much abides; and though
We are not now that strength which in old days
Moved earth and heaven, that which we are, we are,
One equal temper of heroic hearts,
Made weak by time and fate, but strong in will
To strive, to seek, to find, and not to yield.
--Lord Alfred Tennyson--