If Izzy had killed Stede in the duel, it of course would've been devastating for Ed. Especially after the encounter with "the Kraken" that stirred up memories of his father. Especially after he just told Stede something he's never told anyone before--his most secret shame--and Stede responded with support and friendship. It's easy to see how deeply affected Ed is by this.
GIF by @luuuna-rambles
But I also think about the crew here. The night has taken a drastic turn for them as well. It feels like the fuckery was a real bonding activity for them, and minutes earlier, they were celebrating their success. Now, still wearing their costumes from the fuckery, the party atmosphere has suddenly turned deadly serious. As they watch the unfolding duel, is there some part of them that's struggling to cope with that tonal whiplash? This guy's gonna kill my boss, and I'm dressed as a cat... But I got to sing... If Stede dies, what's gonna happen to us--am I gonna die with my face painted green?
The crew has come a long way with Stede at this point. Far from wanting to mutiny on him, they're becoming the crew that's going to help save him from execution. Even if Ed would obviously be most affected by Stede's death, it would be traumatic for them too. Looking around during the scene, it's clear that everyone is tense and worried for Stede. Maybe pirates are "used to death," to borrow a phrase from Pete, but that doesn't mean they take this lightly.
