the great thing about Begins is this is never explicitly stated. Nolan and Goyer left it completely up to the imagination of the viewer whether he had Lazarus Pits or not. You dont see them in the movie, but why would you? So basically they got rid of an unrealistic aspect of the character, yet were still able to remain faithful in that aspect. Ra's death was set up so that they could either bring him back, or not, and it would work either way. They left an opening for him to come back, but made it to where he didn't really have to. Nothing will be left unexplained if he doesn't, but it's entirely possible for him to.
I just find it odd that since Nolan and Goyer have said they dont want to kill off too many villains, that the one villain they would decide to kill off is Ra's al Ghul. I just dont get that.