well, it's been said that
If Joss did carry on with, maybe another movie or something, he bring back all characters (I'm guessing he meant from the TV show, there'd be no reason for The Operative or Mr Universe), meaning he'd probably do a prologue, or quite possibly a sequel with flashbacks to time with those two characters in there.
Hey, according to the link you just provided, Firefly used to be the number 2 seller. That's cool. I'm still gonna wait till February 27th for the UK DVD as there's an extra 20 minute documentary on there, not on the US version (and not deleted scenes, as I'd previously mentioned, we're getting them, but the US DVD also got them) following Joss on the journey from script to screen.