Dent's dead. Whether it was shown or not, I think Batman and Gordon were both positive he was dead. They're not amateurs, and aren't going to just walk away without checking for a pulse.
Besides, the coroner/medical examiners, etc all had to pronounce him dead (THERE WAS A BODY!), presumably before the memorial was held for Dent (Gordon was presiding over it at the very end).
Two Face and Dent are both dead, one in the same.
Besides, as has been said, Nolan isn't going to resort to retconning his own story. That works for comic book runs written and drawn by a large amount of different people over the years...sometimes. Done in a movie series, by the same writer/director no less, is just cheap.
We'll see new villains in a third one, that I can promise you.