During IGN's coverage of the New York Comic Convention '07, the following Announcement was made, courtesy comics.ign.com:

NYCC 07: Whedon Revives Serenity
Mal and his pirates will return this fall.
by Richard George

February 25, 2007 - Earlier today at the Dark Horse panel, publicist Jeremy Atkins and editor Scott Allie confirmed that Joss Whedon's Serenity would see a sequel series published. The mini would take place prior to the movie but likely after Firefly, the short-lived television series based on the same property.

Whedon would once again team with Brett Matthew to write the books. Artist Will Conrad would return to do art and Adam Hughes was tentatively committed to doing covers.

Details were fairly light since the series is still far away. Allie stated that the series would launch some time in the fall, most likely September. The premise would focus on the group acquiring a job so lucrative that it would let the entire crew retire. The pressure of pulling off a job with such high stakes begins to wear away at team, and they slowly begin to break apart as the storyline progresses.

Allie also confirmed that the first script was already written and submitted. IGN will have more details as the release of Serenity nears.