Don't read if u haven't seen THE DARK KNIGHT?

i just saw the dark knight today and it was good. but i have been hearing two-face was supposed to be ther main villian in the 3rd movie but he die in this one shortly after he appeared cuz when he became 2face he got of the hospital he was at and threatened to kill commisioner gordons family but batman stepped in and tackled 2face out of the buildoing and onto the ground killing 2face but if 2face was supposed to be the 3rd movies villian how can they do that with him dead unless they use scarecrow and joker again(if they use joker i know they have to get someone else to play him with heath ledger being dead) but what else can they do if their villian for the 3rd movie is already dead.