Rahs is dead. There's no way he could've survived that crash. And I can't see how Nolan would use the Lazarus Pit or make Rahs immortal either. The only way Rahs the name, not the character, could return is if Rahs Al Ghul is just a name, a legendary name that many are reluctant and hesitant to speak or use because Rahs has been made sort of like The Phantom, as if he is a ghost that keeps walking and living on, but only Batman has seen his face.
The only other way Rahs could come back as a name, would be with Talia. She could fool Bruce into thinking that Rahs has returned, but it is her who has taken her father's place as the leader of the League of Shadows.
The only villain I want back is Joker. I'd hate to see him just go to jail and that's it. Two-Face's arc will be all wrapped up after movie 3, but Joker has potential to be a villain that could appear in another movie. He could be incarcerated in Arkam for movie 3, but return in movie 4, with a whole new face but same personality. Why I say a new face is because we are replacing Heath, you need an actor who sounds alot like Heath and looks like Heath, but I think this time Joker being locked away in Arkam has become obsessed with totally looking like a clown. So, he bleaches his skin white. If Michael Jackson could bleach skin, than why couldn't Joker?