Playing dead in a potential combat situation is a classic strategy to avoid trouble. So much so that both Wikipedia and TV Tropes have pages on the subject. It doesn't get used a lot in roleplaying games, because players are usually the sort of gung-ho people who wouldn't even think of this - it being a defensive strategy rather than an offensive one.
Pull it on your GM some time, and enjoy the flummoxed reaction as she tries desperately to recover from the unexpected brain dissonance.
Yes! K-2 comes in with the wisdom!
Maybe this is the turning point Cassian needed. He can let loose now. He can be useful. He can remember how to fight, how to think tactically, how to not be a danger to himself and his companions.
Unless he was never able to do any of that in the first place. Time will tell.
So, a pacifist. Around a bunch of killers.
After all, he's hanging around an incredibly dangerous killer droid, going in to work with a bunch of killers, all to support another group of killers who could be considered terrorists by any reasonable concept or definition, and in short making sure that he is completely surrounded by massive amounts of death and violence, all because he's a pacifist.
Yep, makes sense to me.
I'm also curious what actually happened in the film here. It sure looks like Cassian killed somebody he was friendly with.
One last thing I just noticed. Wedge wants Cassian to shoot him, and Wedge will be fine as long as his splanch is missed. That's incredibly strong healing for shape shifters. If a shape shifter can recover from being shot, can they recover from the loss of a limb normally? If so, that would explain why a shape shifter was willing to play around with laser swords, and take a tremendous risk.
But now I have to wonder: what are the innards of a shape shifter like? Do they have any actual inner organs? Are the pieces of their body completely fluid, like Odo, or the Terminator? What exactly is a splanch anyways?
Wedge: Look out, troopers!
[SFX]: Pow! Pow!
Cassian: More coming, there's too many!
Wedge: I know how we can both get out of here. You gotta shoot me, buddy!
Cassian: I can't do that!
Wedge: I'll be fine, just aim clear of my splanch! I'll shapeshift into your corpse and escape after they bury me.
Cassian: What if they cremate you?
Wedge: There's no time, just do it!
Cassian: So you actually survived?
Wedge: In the flesh, good buddy!
Cassian: How can I justify being a pacifist now?!
K-2SO: Easy! Don't!