Through The Philosophy of Time Travel, the book written by enigmatic recluse/”Grandma Death” Roberta Sparrow (Patience Cleveland), a complex mythology is unraveled that details how Donnie was destined to die.
In this version of the world, Donnie is imbued with powers that help him do what must be done in order to save the universe.
Again, the version of Donnie Darko we see is technically from an alternate “primary” universe.
In Donnie Darko’s theatrical cut, it all feels like it was destined to happen, almost as if it was a singular time loop that saw Donnie peer into the future, before choosing to sacrifice himself for the sake of Gretchen Ross (Jena Malone.)