Despite being announced as an on-going, it seems that Serenity: Leaves on the Wind
is a six-issue arc. It will be written by Zack Whedon, based on conversations with Joss about story ideas they would have pursued on the show if it had continued.
The adventures of the crew may continue beyond that, but not with Zack Whedon.
I'm in for the first arc, just because I love these characters so much and miss them, but if it continues beyond that, it will depend on who is writing and how much, if any, input Joss will have.