We haven't gotten any actual confirmation that Twilight Alicorn is a thing. For all we know there was a vector error on a sticker.
I also am pretty sure many fans are obsessing about only the negative ways this could turn out.
For instance, if Twilight swapped with one of the princesses for an episode it would be hilarious! I can see Twilight freaking out and not handling the sudden and unexpected change well at all.
If she's a princess, she'd require a whole team of advisors. Not including Spike, I can think of five friends she would trust with her life.
The show is called "Friendship Is Magic". I can't see that changing. DHX has Season 4 on the books. Mike Vogel, VP of Development for Hasbro Studios has said that a short season doesn't mean anything about the longevity of the show.
I would actually find Twilight becoming an alicorn to be a nice way to finish off her training (a.k.a. at the nd of MLP:FiM. On Twilight's friends, who is not to say that they will either A: be sustand by the Elements of Harmony, B: become alicorns themselves, or perhaps C: pass on the Elements of Harmony to another group of friends. There is also B and C.
Of any cause not everything lasts forever, and death isn't a bad things... especially when you have lived a full life.