how does the story truly end ?

Cobb is back in reality because of at least this one basic storytelling clue: Ellen Page's character Ariadne was predictably correct in all her insight throughout the entire movie and there's one statement at the end of the movie in 1st level dream when she escapes the water where she basically said Cobb will be alright. It would not be consistent with her character if she were wrong only  at the end. If you need another clue Cobb's totem was wobbling at the end .. if its not reality then it wouldn't even wobble in the first place. There are more clues  too but I think thats enough for now.je pense aussi qu'au fin du film cétait pas un rever parce que dans tout les reve qu'ill avait ill pouvait pas voire les faces des enfant at aux fin ill ler sa vue .