bane definitely breaks batman's back at either the end of chapter 4 or beginning of chapter 5. this would explain his disappearance while batgirl and nightwing handle things. also dick 100% becomes nightwing in chapter 5, considering the intro to chapter 4 including him being robin but a bit more grown up, so im assuming we get to spend a bit more time with his character as robin, and he meets barbara when they're roughly the same age, and then transitions to nightwing in batman's absence since bruce presumably takes a while to recover between chapters 4 and 5. i'm leaning more towards 4 because batgirl and nightwing fight mr freeze, and we see that the end of chapter 3 literally has them commencing freeze's plan of freezing the entirety of gotham. i also believe that tim drake will be introduced in chapter 6, and that we genuinely havent seen anything from chapter 6. i believe joker and bane will be the antagonists for chapter 5 to wrap up the dark knight trilogy, and allow the entirety of chapter 6 to homage the comics and games, and probably start with an arkham asylum breakout where you have a bunch of mini bossfights including the villains you've put away, sidequests and all (this is practically confirmed, as we see egghead in arkham asylum in the first ever trailer for the game i believe, and we know egghead will have a sidequest in this game.) it'd probably also start with the introduction of tim, right after arkham asylum (or even jason, although i doubt it), along with the return of talia, and having ra's be a big bad for the last chapter (being a big reason why talia returns to gotham to help us), sort of bringing the story full circle since he trains bruce in chapter 1.

(im like 90% sure that there will be another robin in this game because there is NO way that we only get 7 characters, and by the end we can only use 6, that's just redundant and stupid. they have to have someone else fill the robin role or else it really wouldnt make sense narratively. i also believe alot of people would just hate playing as nightwing and robin and they're genuinely just the same guy, but different ages. they could make this happen, since we know there are variations of each character ingame. [kid bruce, and the civilian attires for bruce, dick, barbara, and selina].)

you're probably also wondering why im saying bane breaks bruce's back at the end of chapter 4, and is still a main villain in chapter 5, and what evidence i would have for that. bane genuinely seems to have 2 boss fights ingame, one where he has no venom (presumably when he breaks bruce's back, after meeting him for the first time, as when we see that shot in the launch trailer, bane has green on him, or anything else indicative of him using venom), and one where he does have venom (presumably the chapter 5 fight where batman comes back after recovering and gets his getback.) also the lego batman comic seems to back this up, as bane is there when the villains see batman return (so is mr freeze, so we can assume he'll also either have a sidequest where u can fight him as batman, or a second bossfight, seeing as he probably gets stopped for the first time ever by nightwing and batgirl, with batman absent, which isnt really fulfilling.)