Spoiler i know, it was taliya that escaped, not bane. yet the entire movie, they kept showing a child with a perfect face escaping, which lead it to be very predictable. at the same time, if the folks in the pit mentioned that it was a girl, then it would have lead to a bigger deal. however, they kept saying 'its a child' and thats it. point being, it made it far more predictable. ra's al gul and taliya didn't free everyone from the pit. there were those who still told the stories to wayne. and if they did come to save everyone from the pit, then it doesn't make sense to leave a few behind. and they could have pulled the trigger when bruce was in the pit as that would have been far more torturous as he is sitting it out and watching his entire city burn. i mean, when batman came back, bane said 'impossible!' meaning no one was expecting him to come back, meaning they would have blown the place regardless of if batman was there or not. which still stands my point regarding why they had to wait to blow it up.