How is his death as inconclusive as the end of Halloween?
At the end of Halloween, Michael Myers' body is gone. Vanished from where he fell. At the end of TDK, Harvey Dent's body remains laying there for 5 minutes, with a memorial service following.
I said it before in the other thread - if Harvey was alive, then why the hell wouldn't Gordon or Batman be trying to help him? Instead, they stand around for an hour talking about his legacy and how to keep it alive. If he's alive, he's at least critically injured, and needs immediate medical attention.
Plus, what happens to Dent if he's alive? Gordon hauling him to Arkham in secret seems to be everyone's pet theory. But that's impossible. Batman's taken the wrap for Harvey's crimes, because Gordon can't keep a lid on the whole dirty business. With Dent alive, he'd still have his hands full keeping a lid on it, and Batman's sacrifice would be for naught.
If Nolan wanted the death to be ambiguous, there'd be no body. Dent is laying there dead as a doornail; Batman (or Gordon, I forget) even turns his head over to the good side. You don't think he'd hear a heartbeat?
But most importantly, Two-Face doesn't need to appear again. He really doesn't. Anything beyond this would do nothing but cheapen TDK. Nolan said everything there needs to be said about Two-Face in this movie. Where would he go from here? He's gotten his revenge on Maroni, he's judged Gordon and Batman, he won't be going after the Joker (since I doubt the Joker will be returning) - all that's left for him is to be the generic gimmicky "I rob places with "2" in the name" criminal.
I'm not trying to be a jerk here, but come on. These theories wouldn't exist if this wasn't a fan-centric movie like Batman. You didn't hear people going "I think Jack is still alive" after watching Titanic. You want to wish for the best because you want more because you love these characters. But you're coming from the comic standpoint where these characters have been killed and ressurrected a million times in 70 years - because they have to, because the comics need to recycle villians to keep sales up. Movies aren't like that; if you get three movies in a series, you're lucky. Nolan doesn't need to reuse any villians, unless for throwaway cameos (like Scarecrow) or if the story really calls for it. Two-Face's story is over. It was great; you don't want it dragged on.