when you say Twilight Sparkle will outlive her pony friends as an alicorn, she could simply go back to the humanoid world, assuming it brings her back to her high school days, allowing her to live a finite life as a humanoid with her other friends. Perhaps even with Sunset Shimmer.
How did we know the mirror would bring her to an age-appropriate high school scenario in the movie? Equestria Girls could’ve taken place in a nursing home.