You cannot say with 100% certainty that (SPOILER)Two-Face is dead and cannot come back in the sequel. His "death scene" was ambiguous enough to warrant a possible return, along with several people connected to The Dark Knight, including a producer and Aaron Eckhart himself, saying that he may not be dead and could possibly return for the next movie.
(SPOILER)Well if Selina Kyle could survive a seven story fall I guess Two-Face could survive a four story fall.