There is actually, IMO, a very good fanfic out there that is about that. It's called "The Sacking of Port Royal," and I'm thinking it may be posted at the Black Pearl Sails fanfic site. That idea makes for a wonderful story and would make for a great trilogy, especially since we see how Will must struggle with many things and take the Hero's journey. Your idea is much more mythic, which is something that I think existed in the first movie.