I think it'd just be completely different movie without Talia. You'd pretty much have to lose the whole Wayne Enterprises energy project subplot without her. So the movie would lose the aspect of Bruce's wealth being turned against him, along with the element of Bruce attempting to save the world outside the cowl but having to live with the paranoia that "one man's tool is another man's weapon". All of which are great thematic and character touches for Bruce.
Then there's the factor that it'd be kind of strange to have a movie dealing with the League of Shadows while not including a living al Ghul in the storyline. I think, given our knowledge of the mythos, Talia would feel missing from the story if she wasn't there. You'd also lose some of the legacy themes which are important, unless of course they actually made Bane the son of Ra's al Ghul which...could've potentially rubbed more fans the wrong way. Either way, given that Ra's was dead and there was no Lazarus Pit in this universe, I thought him having a child was the purest and simplest way to get across the idea of his "immortality".
I also thought it was kind of clever how Miranda was a red herring for Bruce and effectively becomes his "new Rachel", the person he hangs his hopes on a normal life for. It was not a bad way to divert attention from the impending BatCat happy ending, but it's also an extension of the Bruce/Bane dark mirror aspect as Miranda is in many ways a dark mirror of Rachel.
Overall I would say that the movie could've worked without Talia but I do think the best and richest version of this particular movie does include Talia one way or another. I agree that it would've been great if she could have been introduced in BB, but alas, there are many reasons why that didn't happen.
