It's obvious that her having those alicorn (state) powers is similar to Aang(from the Avatar: The Last Airbender series), she's obviously task in keeping all 3 species in Harmony and make everyone stable, which I can see a comparison to the avatar in the ATLA series, being task in keeping all the nations in balance and peace.

And (for those who don't know) if the avatar had disappeared, everything would obviously fall into chaos, and so would equestria if sunny with her powers, vanished without any trace, which I think this might've how twilight sparkle vanished.

Unless if she place your whole body and soul into the crystals, it's possible that sunny might find a way to contact her through the crystals, like Aang contacting her past lives in either special locations that are high in spirit energy, of with certain artifacts (like in the ATLA comics after the series) for guidance .

Which imo it be so awesome if they do that with sunny contacts her for any enlightenment, if they do it right of course.