As a Game Master, you should always prepare some adventure material so that you have something to run when your players assemble.
Q: How much do you need to prepare?
A: Pretty much any amount greater than zero will guarantee that the players won't get through it all.
Not too long ago, the Comic Irregulars mentioned the idea of catching a player up on what they missed by having the other players try to recall the details of the adventure.
Since Corey/Luke and Ben/Chewbacca both missed a few sessions, we see them asking the other players about this section of time.
And, lo and behold! The GM wants to run a new adventure that starts 30 years later on Tatooine (Episode VII), and the players want to go back and talk about what they did when the other players weren't around.
The idea of saying, "let's put the main campaign on hold while we are missing two of our players and instead run a side adventure" is a wonderful way of handling the lack of two players. It's also a wonderful segue into Rogue One — which looks like it will be that "side adventure", expanded to cover the entire group this time.
Re-reading the old stuff, we see that R2 got the plans back in #451, and comments about telling the difference between an inert rock and a giant doomsday weapon. Then, in #497, he practically lays out the future story by describing hiding the existence and controls for the weapon, having Kamino create it, and having a meaningless invasion and war to distract people, while inaccurate blueprints show nothing but a rock and memorial.
During this time, Ben was playing Obi-Wan; he even looked at the copies R2 had. So it seems odd here — did Ben really forget that session, and think that the plans were recovered while he was away?
Well, all that requires is that a player forgets a major point of a long-running campaign played over a decade of real-life at this point, which is actually
very common easy enough. Trust me on this one.
Ha! I knew Episode VII was always meant to start on Tatooine! I knew it!
Well it does look like this is leading to some sort of flashback, and the GM does have a new campaign he wants to run... but those two things seem to be at odds.
Will Rogue One be story time with Uncle Pete? Or will Corey and Ben get a chance to play through that adventure themselves?
Time will tell.
Corey: So how did you get the Peace Moon plans?
Sally: It was a pretty intense adventure, first learning that the Empire was actually building the superweapon in it.
GM: Do we really want to go into this now? I'm ready to run a whole new adventure. It starts 30 years later on Tatooine—
Ben: Actually, I'd like to hear this too. That was those sessions you played while I was away, right?
Pete: Yeah. We played... four sessions before Corey joined, and then one more before you came home, Ben.
Annie: We didn't really want to play the space campaign without you. But we did want to play something.
GM: I'd prepared an adventure already, so I suggested creating all new characters.
Jim: Yeah! That way we got to play the same campaign without you there, but without playing it without you.