Swapping out-of-game favours for in-game actions kind of breaks the usual compact of a roleplaying game, but that doesn't necessarily mean it should be verboten. It can lead to some cool moments and as long as everyone's having fun... well, that's why you're playing the game in the first place, right?
Commentary by memnarch (who has not seen the movie)
Uh oh. Finn's got it in his head that he needs to Independence Day the cannon. I'd say that this is probably where we see the end of Finn, except for two things. I think I remember seeing Finn on the movie box covers for the 9th movie, and here Jim and Ben are talking about stopping him.
So really, the question is "How is Finn going to be stopped?". Is Ben going to argue how flying in the targeting beam damages the craft enough that Finn falls out? Will Rose do something like shooting Finn down?
Hmm, between those two ideas, I think maybe the second is a little more likely. I'd wanted to say that the first was until I thought through how the second option would work. If Finn's skimmer is knocked down by Rose somehow, then that means the cannon will still fire. And if the cannon fires, that means bad things likely happen to the Resistance base. And since the rest of the movie has gone that way up until now, that feels like the safer bet.
Transcript
Finn: I make a beeline for the cannon. Ramming straight down the barrel should take it out.
Poe: You’re going to sacrifice yourself?! Nooo!
GM: Hmm.... <roll>...
Finn: I switch my headset off.
GM: <scribble scribble>
[SFX]: Whoom... {the battering ram cannon continues intensifying the targeting beam}
[SFX]: Sssshhh! {Finn’s speeder lifts its ski and flies directly towards the cannon}
Finn: I’m sorry, Gil. I couldn’t bring myself to kill him. Guess I’ll be seeing you soon.
GM: Jim, a note.
[SFX]: Whoom...
Poe: Rose! We can’t let this happen!
Rose: What do you want me to do about it?
Poe: Stop him and... I’ll do you a favour. I’ll take your music students for a whole class.
Rose: What?
Poe: A guest lecture on the physics of music.
Rose: That... would actually be cool.
Poe: Everybody lives, Rose. Just this once, everybody lives!
Rose: Excluding that speeder pilot earlier.
Poe: Well, he’s an NPC.
[SFX]: sssshhh! {Finn’s lone speeder is dwarfed by the cannon as it hurtles headlong down the targeting beam towards the gaping muzzle of doom}