One of the things I didn't like about the movie was how Harvey Dent's fall from grace was treated by Batman & Gordon as such a catastrophe in terms of their fight against organized crime. Like, if any of the public ever saw the slightest tarnish on Dent's reputation, it would throw the masses into such despair that they would never recover. I didn't like that they seem to hold so little regard for the people of Gotham that they need to be lied to just so that they'll go along with the right thing.
For that matter, I wouldn't think it was Dent's incorruptible reputation that made him so unique but rather his fearlessness. Like Gordon said in Batman Begins, what they really needed was a D.A. brave enough to prosecute without fear of mob reprisals. In that respect, it doesn't really matter how Dent died. The fact that he died at all is what might terrorize the people into submission to the mob again.