Twilight Sparkle, the newest princess of Equestria, is immortal.
Pinkie Pie, Equestria's greatest party pony, isn't going to let a little thing like death get in the way of her friendship.

[I'm only up to season 5, so please forgive any changes I make to cannon]
[I started a similar story with the same premise ages ago, but I wanted to come back to it from a new angle]