Except the Warden wasn't the protagonist. He had nothing at all to do with the story of DA2.
Think of it like the end of Pirates of the Caribbean 2 (because that's the example that pops to mind). Barbossa walks down the steps with an apple. Screen fades to black. OH WOW COOL. Most people would call that a cliffhanger.
But it's not. It's introducing this new element to the story that will be expanded upon the next movie. It's a hook to get you interested in the next movie.
Same situation. The Warden is mentioned at the end, so that you'll be interested. "Ooh, why has the Warden disappeared! What's happened?!" But the main plot has been resolved.
On the contrary, a cliffhanger is an ending which intentionally leaves the audience in suspense. I wasn't referring to the warden, I was referring to Hawke, who IS the protagonist of the story, and has disappeared.
PotC 2 is the definition of a cliffhanger ending- the point was to leave the audience in suspense for the next movie, which had already been filmed. Another example would be the matrix 2 or back to the future 2. The main plot has been resolved but the fates of the protagonist and the results of their actions are deliberately left hanging to encourage people to see the next movie.