I actually disagree. The movie indicates in a not-very-clear way that DJ was expecting some type of reward (not just Calypso) for ferrying dead souls.
The movie never implies that Will needs Elizabeth to remain faithful in order to not be squid-faced. What the movie states is that DJ chose to become bitter and abandon his post, cut out his heart, and become squid-like.
I have no doubt in my mind that Will would never have gone this route, that if Elizabeth had chosen to not wait for him (if she hadn't run after him on the beach), Will would have remained human looking, and would have honored the agreement that binds him to the Dutchman.
The only thing unclear in the movie is what happens after the ten years are up. TnT had lines in there that were meant to indicate Will is going to be free from the Dutchman in ten years, and because of unfortunate editing, it is not strictly canon, but I figured it out on my own that the curse would be broken, so I consider it canon anyway. 😄
By the way, TnT have hinted that movie four might take place before the ten years are up, and they seem to have a few ideas for adventures in mind for Will and Liz (and of course Jack). Now if we could just get a good story and everyone signed up...😄