**Edit** I just saw Savvy's post, so I don't want you all to think I was over-writing her fabulous post. I worked for twenty minutes on this post, and I'm far too lazy now to change it. But Savvy, that post of yours was great!***
The quote about the dress is this: ""Elizabeth is now free of the dress. Free of whatever constraints might have come from the dress. Like the corset in the first movie, it's all about what Elizabeth is wearing"
It's quite possible that it means that she's a pirate. Or it could just mean that she is no longer bound by the social constraints. That doesn't mean, however, that Will is by the wayside because of that.
Quite the contrary; remember, he donned more piratey clothes himself. I think that what the writers here are trying to say is that the break from high society has finally happened. It fractured a tiny bit in the first movie, and now both Will and Elizabeth have lost that last tiny fragment that is keeping them chained to Port Royal.
Gov. Swann lost his wig, the symbol of his power. So did Norrington. Everything these characters are wearing (or not) is symbolic in some way. Although, to be honest, Gov. Swann didn't have to have his wig removed to act quite piratey himself. 😄 I love that character. *sighs*
Also, I don't think that part of Elizabeth that is good and decent, with a moral compass, is dead and gone. I think it was lost to the Shadow aspect, and eventually she will come to terms with both sides of her personality. There is no 'death' of her character, but rather a unification, where Elizabeth will find out what her true self is.