What JF said is definitely the best idea.

However Will and Elizabeth's story does not necessarily have to be over. If T&T really wanted to add those characters into the story, there are potential plotlines that could work. Will and Elizabeth could go with Jack and Barbossa to the FOY. Now I admit that Disney is not very interested in these two's story and it would be a little hard for them both to come back, but it is possible. I for one would be very happy to see Will and Elizabeth back in POTC4.
