What happens when the entirety of Equestria, if not the fate of the whole world, relies on the shoulders of just 6 heroes and their companions? Did anyone dare to question what would happen to the future if those heroes can no longer bear the burden one day, and those believed vanquished rise again?
Twilight Sparkle, Starlight Glimmer & Spike have witnessed the outcome of such dependency; a future without the bearers of the elements. Chaos, darkness, conflict, fear, anguish, sorrow and ruin. And their only response to that was acceptance, rehabilitating Starlight Glimmer to be part of their ranks so perhaps she could make a crucial difference.
But there are many more events aside from time manipulation that can cause such dark times. The heroes triumphed over many fiends and challenges that brought everybody to the brink of doom. Even those they reformed narrowly managed to save their land from rule through fear and intimidation by the former changeling queen's hooves.
Ultimately, it does not change that time could be running out for them and this world at any minute. There might be no future in anything they believe to have accomplished while everyone else spectated powerlessly. False hope sown by narrow minds only reaps exasperation after all. But all inhabitants of this world deserve something else, something nobody could never achieve on their own.
A future of lasting harmony.