She actually came back in Equestria Girls, but even if she was never seen on anything MLP related again, the fandom would have kept her alive. To paraphrase pro wrestler Chris Jericho, They will never, EEEEVER take our Derpy away!
So I finally got to see that episode, and I just have to say that between that episode and today's, my heart's just bursting with joy that Derpy is back. I missed her. This is so adorable, and cute, and perfect. ^___^