I think there will be at least one more expansion for this game, even if it is just a "small" one, like the Arkham expansions. There are several more characters I think the game needs (it just won't be complete without Anders), and themes it can follow the Final Five and Daybreak are just two of them.
This game is still a successful seller, and we play it weekly still at our store (which I think in turn makes it a successful seller). If the game is good, it will outlast the property's tv run. Pegasus was still a big hit, even though BSG was off the air for 6 months. I think a new expansion will be just as successful, and we might see one next year at Gen Con.
I guess/hope that there will be two more "regular size" expansions, and if you think about it it makes perfect sense. [spoilerS AHEAD!!] The basic game covers season 1 of BSG up until the discovery of Kobol and the beginning of season 2. The Pegasus expansion covers season 2 - especially of course the arrival of the Pegasus - up until the discovery of New Caprica and the exodus from the planet which happened at the beginning of season 3. The next expansion could cover the events of season 3 - with a focus on the Final Five who will also name the expansion - and the last expansion (called "Daybreak") could cover season 4, the discovery of "frakked earth" and finally the battle for the Cylon Colony. A new additional game board for the renegade basestar from the Cylon civil war would also be a possibility.
Also there are a lot of characters that change significantly during the course of the series - Lee for example resigns and becomes a lawyer, Baltar becomes a cult leader - and that should be taken into account by releasing new versions of character cards.
And there are enough other motifs and concepts from the series to fill at least two more big boxes...