This is just an idea I had after the season 3 finale aired, and before Meagan Mcarthy banished the idea that Twilight would outlive her friends.
100 years after finding her destiny and ascending to the Princess of Magic, Twilight is faced will the most dire and tragic of foes: Time. Twilight is immortal and will linger on, but her friends can't stay with her forever.
How would she have handled their passing?
And is Celestia to blame?

Are the many misadventures and perils that face our favorite collection of ponies merely random occurrences? Or is there something much more sinister afoot? A new evil has been unleashed upon Equestria, but not from their own world. No, a super powerful organization calling themselves the Continuum have had their eyes on this world for some time. Now that one of their own members is on the magical soil, who's to stop them from achieving their goal?

First MLP fic. Rated teen for language and violence. WARNING! Characters WILL die.