What if in the original timeline Cooper goes into the black hole and dies there. Murph never receives any message. They do not solve gravity. Plan A fails. Everyone on Earth dies. Brand (Anne Hathaway) is the last member of mankind still alive. On Edmunds' planet she grows the fertilized eggs they had brought with them on the Endurance. She succeeds with plan B. The new humans live on that planet. Eventually they become more technologically advanced than we were back on Earth, and at some point in the future they attain such a deep understanding of the universe that they evolve to live in a higher dimension, the bulk. There they perceive love physically, love has a tangible existence in this higher dimension. They perceive the love that linked humans back on Earth a long, long time ago. And then out of love they devise a way to allow these humans to keep living too, some of whom were their ancestors, their great-great-...-great-grand-parents. They perceive the strong love that linked Cooper and his daughter. They realize they can save the humans who lived on Earth by enabling Cooper to communicate with his daughter from inside that black hole, through the link that bound them together. Once Cooper succeeds they send him back near Saturn through a wormhole, to allow him to see his daughter one last time. Brand allowed the future humans to live, Cooper allowed the humans back on Earth to live. In the end Cooper leaves to reunite with Brand, in a sense reuniting humanity together: the future humans who couldn't have lived without Brand, and Earth's humans who couldn't have lived without Cooper. It was love that had brought Brand to Edmunds' planet and allowed future humans to live, and it was love that allowed Cooper to save Earth's humans