Pinkie fell the furthest in moral terms, in my opinion. That made her repentance, literally at the moment when it was already too late all the more poignant.
Still, whether or not she was fully aware of it, she had left behind her all the tools and clues Littlepip needed to save the world. So, in the end, she kept the faith and did her duty to her five friends and to all of Equestria. I can think of worse ways to go.
Behold! Behold you ponies! We have warned many times! I have you told you of my dreams! My nightmares! And what I saw! We, the 4014s have experienced dreams! Dreams that you will all be taken by the shadow! The Shadow! The shadows of Satan and his demons! Of evil and of immorality! Death is coming! Now look at what you all have done! Your world is now suffering what we have tasted as well!