I wasn't too surprised by what happened but it still kind of bugged me. Spoilers ahead. (Seriously, if you plan on watching the episode, don't read any further.)
Bixby was nothing more than a plot device from the moment she appeared. That sort of thing isn't unusual but it was so blatant and ham-handed that it was distracting.
She was put in danger in the first episode and conveniently in the right place at the right time to witness the reveal of the Chosen One. She was conveniently in the right place and time to be wounded in the next angel attack. She conveniently blabbed about the Chosen One in public to set up the main event of last night's episode.
Since Whele had the other smallfolk who witnessed the Chosen One's reveal killed it's not surprising that he killed Bixby when he had the opportunity (Bixby had been under Claire's protection before). But it still felt a but like Whele was kicking the puppy. We already know he's not a good guy but let's have him kill the girl so there's no doubt in any viewer's mind.
So next episode Alex will blame himself for her death (since it will look like she died of her wounds) and be sad for a moment or two before the next crisis pops up. Bixby may get mentioned occasionally when Alex needs to feel the weight of being the Chosen One. ("I'm supposed to save humanity but I couldn't even save Bixby. I has a sad now.") Maybe his magic markings will tell Alex that Whele killed her or GhostBixby will show up in a vision to tell him. But otherwise, Bixby is gone down the memory hole.
It's too bad because Bixby could have been used to show Claire Riesen what life was really like for the lower castes. Claire is already shown to be a reformer and her relationship with Bixby could have developed that aspect. Maybe have an episode where Bixby shows a disguised Claire around the slums of Vega. But we're not going to get that.
Poor Bixby. You were doomed from the beginning but you still deserved better than what you got.