Seriously, what is so freaking special about the Warden that people just can't let it go? He had no personality except what the player makes up in his head. He had no voice except what the player makes up in his head. He did his thing, it was epic, he stopped a blight. Very few wardens get to do this. Even the Orlesian warden (which the player can play) doesn't do anything any other warden commander would be capable of doing.
Since his personality is entirely head canon, there's no way Bioware could possibly give him a presence in a game featuring another protagonist that would be true to everyone's vision. 10 different people are going to have 10 different perceptions and no doubt no matter what Bioware did, all 10 would insist "My warden wouldn't do that".
The whole 'disappearance thing' works for me. It falls right into my own head canon and allows me closure in my own mind. I don't need Bioware to say X happened to Neria. Because no matter what it is, it's going to fubar it up in my head.
Be careful what you wish for people. The worst that could happen is you find out.