GMs need to be flexible in their plans, of course, but it's a real skill to adapt an entire session's worth of adventure planning when a player doesn't show up, and things need to be modified to make sure the remaining players can advance the quest without requiring that player's character to be present for something crucial.
As a general strategy, it's nice to be able to plan your adventure so that important things can be achieved in multiple ways, by different characters. This can be tricky, though, when roles are hyper-specialised, such as in settings like cyberpunk, where one character may be a netrunner while another is a street tough and another is a business executive.
Commentary by memnarch (who has not seen the movie)
Still processing events; that's entirely fair. I've also seen similar things with the groups I'm around with people not wanting to disrupt the game if they've got things in life they should deal with first. The GM usually makes some quick plan adjustments as well, if there's still enough people around to play that week. It feels like the "significant events for the aerial battle" could be a reference to something, but I can't decide if it's stuff in the movie that's not going to make it in now (no more focus on the aerial fighting) or old movie script stuff that wasn't used (like Luke Starkiller in the very first movie).
And of course it's a 50% chance; they're either dead, or not. Given the fighting end results in Episode IV, I bet that Allan, and maybe Snap, are the only ones who make it through the battle here with intact X-wings. Really, the Resistance should have sent a lot more fighters to this engagement. Maybe even some old capital ships as well, and then we could have had an explanation of why the Finalizer hasn't shown up.
Zeppo: Hi! We’re here, let’s get started.
GM: Where’s Corey?
Rey: Yeah, he’s not coming. He’s still processing what happened. He said we should play, though; he’s sorry for disrupting the game and didn’t want us to miss out this week.
GM: Hmm, okay. I did plan significant events for the aerial battle, but I guess we can concentrate on action on the ground.
GM: So let’s see. The dogfight is ongoing above Chewie, Finn, Rey, and Zeppo.
[SFX]: Pow! Pow! Pow! Boom! Pow! Boom!
GM: You see two X-wings hit. Counting, it looks like they’re down to half strength.
Rey: So there’s a 50% chance Allan and BB-8 are dead already.
Zeppo: Nah. If I know Allan, he’s impossible to hit!
Chewbacca: I don’t believe you’ve ever met him.
Zeppo: See how difficult he is to engage?!