The Dark Knight Rises: The Official Novelization by author Greg Cox delves into the Jonathan and Christopher Nolan screenplay a little closer. Original rumors had Heath Ledger’s Joker make a cameo via unused footage from 2008′s “The Dark Knight,” but it panned out as such. Warner Bros. Studio later confirmed it was just a rumor. Cox provides better details and lets fans know about the shady and ambiguous fate of the Joker. Here is the exact quote from the novel .
Now that the Dent Act had made it all but impossible for the city’s criminals to cop an insanity plea, it (Blackgate Prison) had replaced Arkham Asylum as a preferred location for imprisoning both convicted and suspected felons. The worst of the worst were sent here, except for the Joker, who, rumor had it, was locked away as Arkham’s sole remaining inmate. Or perhaps he had escaped. Nobody was really sure. Not even Selina.