Remember that maxim when running a game. If a door closes, because the heroes have been unlucky or possibly even if they've done something stupid, you can always make sure there's another door ajar somewhere. Think of a way for them to save face and complete the quest.
You don't necessarily have to give them a way out. It depends how gritty and deadly your game is. But just remember that you always can.
Commentary by memnarch (who has not seen the movie)
Uh oh. That's pretty much what it'd be if someone got in an accident or suddenly became ill. Hopefully it's nothing so major that Corey never comes back to the game, even if BB-8 needs to be GM-ran for a time; he's been an interesting character. I guess this is one way to have BB-8 take more of a back seat role like R2-D2 did in Episode IV; this seems to be what happens to the mascot-like droids in Star Wars during the climax scenes.
At least Jim's still upbeat about the situation.
Snap Wexley: I got one behind me! See it?
Jessika Pava: Yeah, I’m on it.
GM: A point defence cannon fires missiles.
Jessika Pava: Furillo’s been hit!
BB-8: Oh crap.
Allan: It’s not that bad! Just watch out for ground fire, BB-8!
BB-8: No, I gotta go. Sorry everyone.
Snap Wexley: We’re in the middle of a fight!
Snap Wexley: Geez. I wonder that was about.
Allan: When one door closes, another opens. More enemies for us!