Though Cameron presumably could have taken the franchise in a different direction, Worthington and Saldana reprising their roles as Jake Sully, the disabled ex-Marine inhabiting an alien body, and Neytiri, the Na'vi huntress, suggests that their story will remain front and center.
Given that "Avatar" still holds the record for worldwide gross with nearly $2.8 billion, and that Worthington and Saldana are the film's main characters, it's not particularly surprising that they've signed on for the sequels. That said, three more movies is a long time to spend on Pandora, for the actors and for audiences, so it will be interesting to see whether "Avatar" fatigue sets in and with whom.
Cameron is planning to shoot the three films concurrently in New Zealand (taking a few pages out of Peter Jackson's playbook for his "Hobbit" trilogy) beginning early next year, with an eye toward releasing the first sequel in time for Christmas 2016 and the other two in late 2017 and late 2018.
Since the release of the original film in 2009, however, release dates for the sequels have shifted repeatedly, as have the screenwriters and even the number of films. The original plan was for two Cameron-penned sequels, with release dates in 2014 and 2015. (Josh Friedman is writing the first sequel, Rick Jaffa and Amanda Silver the second and Shane Salerno will close out the series.)
Having secured its two stars, though, the franchise has taken a few steps back toward the big screen.