Hmm, that's fair enough. I mean, Goyer did give that quote to EW back in 2005 about the sequel was going to set up Harvey Dent, and the third film was going to feature Harvey getting scarred by Joker. Maybe that was just him spitballing his own thoughts to the press. I'm sure Nolan yelled at him for that.
Personally, I think that living through each film organically proved to be the right move. If they had set definitive for parameters for a third film that necessitated the return of The Joker, they would've been in a very tough spot after Heath died. Star Wars could be in a situation like that now with Episode IX and Carrie Fisher, we'll have to see.
I still personally think the League of Shadows returning was something they always had in their back pocket. It was just too big a part of the first movie to simply ignore if you're trying to wrap things up. I always saw Bruce quote Ra's' "criminals aren't complicated" line in TDK as a subtle way of keeping that thread present. Also, fun fact- Talia is referenced on the bonus features disc of Batman Begins in the character profile of Ra's. There's a quote from Nolan too where he says the first thing he immediately knew about the third film was that he wanted to see the League of Shadows story line come back.
My gut feeling is that even if Heath had lived, it's very likely that the story they would've developed would've been largely similar to what we got. It just would've also found a spot for The Joker too. I think his storytelling instincts, along with Jonah and Goyer's would've likely led in a similar direction anyway. And Ryan, I know you would've preferred a smaller scale third movie- you can't deny that Nolan has been on a trajectory of going for bigger and bigger scope with his films. TDK-Inception-TDKR-Interstellar...each film is bigger than the last there in terms of scale, and it's still happening now with Dunkirk which once again is going to be have a bigger majority of IMAX footage than all his films. I think it's a stretch to assume that if Heath had lived we would've gotten something that was smaller in scope than TDK. There is no doubt in my mind that Nolan would've always looked for ways to make the film visually grander and more epic in scale.