Dear Princess Celestia,
What if you became evil? How could it happen? Why would it happen? What would happen? What would become of Equestria? What would become of the elements?
Your Faithful Student,
Twilight Sparkle.
Dear Twilight Sparkle,
A good question my dear Twilight. If I were to become evil, what would happen? I hope to answer this question for you and me, hopefully preparing you in case it does happen.
If I became evil, I would probably want to create infinite daytime, meaning nopony can stop working - this leads to slavery. So if I felt a lust for power, I would most likely fall to this. There are many ways for me to become corrupt into a being of disharmony; disharmony contagion, need for power, tragedy.
The things that would happen to Equestria could be drastic, and possibly leave a huge wasteland in the middle, with my knowledge of scientific advancement which I am not allowed to share. So overall, Equestria would be doomed if I was given enough time.
The elements of harmony should work to purify me once more, but it depends on how evil I become as I did once wield them myself. They would probably try to purify me by themselves, probably to no avail though.
Princess Celestia.