I believe the Libertine wasn't all that widely released. If I remember correctly, one theater around here locally played it, but none of the others did, and I live in an area close to two larger cities.
I would think DS would be groomed to be a franchise, if Depp was willing to return to the character like he did to Jack Sparrow, which would up its odds for box office take. DS has what it takes to be a franchise film.
And by the time DS would come out, another Pirates will likely be on the horizon, since Depp's willing to come back for a 4th film, which would only increase the Depp awareness factor in the public. While Depp didn't do as well in the box office before, Jack Sparrow definitely made the public aware of him, and I don't see that going away in the next few years.