From any standpoint I believe that it is important for the Warden to reappear; if not in Inquisition in the flesh, then at least in some reference that explains his or her location. Most of us played DAO several times and had several Wardens, possibly with differing endings. But nonetheless, the Warden character was the prime focal point at which the game ended. In DA2 there was minimal reference to the Warden, but the implication was that (s)he was still around somewhere. It would be unacceptable for the character to now just drop of the face of the planet with no explanation. For me, personally, I would sadly miss my Warden and would love to see her return in the flesh.
From a story-telling point of view, not addressing the status of the Warden would, quite frankly, result in a terrible story. Anyone that understands story structure, knows you cannot make a character carry out an action ( i.e. disappear) without giving a cause and a resulting effect or a foreshadowed effect. For example if a character disappears you can justify it by saying it is within their character to do so or another scenario is to say the character was taken against their will, in the latter scenario you have to address the circumstances surrounding that event and/or the effect of them being taken, you don't have to do it right away but you have to do it or else what is the point of that bit of the story.
Example:
Person A and Person B are having an intimate discussion about the state of affairs of their nation, Person A an avid supporter of the royal family is arguing that they should be allowed to rule as a monarchy, Person B counter-arguing that the nation needs a ruling body elected by the people not a single family that rules forever. When suddenly Person C swoops in through the window and slaps Person A, mid-sentence, across the face with all the force he can muster from his stocky, 6'4" frame and then jumps back out the window again. Person A finishes up his proposal of a royal family stating that a single guiding hand is what the nation needs right now and Person B counters that a single hand is needed but a hand elected by the people.
See that ^. Without the context of Person C being a ghost that scenario makes no damn sense. You would expect some response wouldn't you from A and B but nothing, not even a 'swooping is bad'. Ergo Thedas must respond to the Warden being gone/not present to deal with the Inquisition and if not Thedas, then Ferelden and if not Ferelden, then the one he romanced would most certainly have something to say about him. Of course this only applies if the Warden has made those connections and isn't dead.