I think a sequel is more necessary, but technically aren't sequels continuations anyways? Or are we referring to the continuation as in "5 days later dah dah dah happens..." ?
Here's how I think "BB2" should start out...
A year has passed in Gotham City and Batman has still not caught the man responsible for "The Joker" calling card. He however has gotten leads and tips by thugs and ever so closely is almost near to catching the infamous criminal.
Meanwhile... the mobs of Gotham are trying to restore order after Falcone's empire collapsed. Rupert Thorne and the Maronis are still fighting over ownership like two lions over a dead zebra carcass.
Lt. Jim Gordon is now responsible for taking on a new partner named Harvey Bullock.
Harvey Dent has now taken over at the D.A.'s office.
A desperate man named "Jack" who is a former stand-up comedian is dangling from a thread. He's got a pregnant wife, he's about to be evicted from his apartment, he's got no money, his life is crummy, until he gets his big break as "The Red Hood." But after an accident at a chemical plant he becomes the face he always sees on his card deck...
Then, you could have a flashback cameo by Thomas Wayne, Scarecrow could cameo if you want, The Penguin comes in for a brief cameo, and then give Bruce a new love-interest and have Lucius come up with some new toys for him and you got yourself a hit.