1Up's played Ratchet & Clank Future: Quest for Booty (drops next week on the PlayStation Network) all the way to the end, and got the above teaser screen. Insomniac has said nothing, but it's doubtful they'd tease anything other than a full retail release this far out. 1Up notes that it looks like Insomniac will be switching between Resistance and Ratchet titles every other year which is definitely pulling its weight for the PS3. Ratchet & Clank Continue the Quest in Fall 2009 [1Up]
@Wolfers: There's a difference between a franchise (Mario, Zelda, Final Fantasy) and a series (Halo, Metal Gear)
I always hate games (or movies) that don't resolve the story. This isn't the same as Episodic games which by their very definition will be continued in future games, or a series that's already planned to be multiple games (Xenosaga for example)
Each game (or film) should be able to stand on its own merits storyline wise. If I were to buy this game, and then be "surprised" at the end with a "To be continued" I'd be pissed.
Just like when I go into a movie expecting an ending and instead get a cliffhanger.