Thank you all for your feedback and help!
In patch 8 at least, the masks also remained hostile after I killed Ethel, and I had to run away through the portal and return afterwards before they would stop fighting and talk to me.
When I reported this as a bug, I was told it was intended behaviour which seemed bizarre to me as surely only people who already knew a mask could be saved would bother running rather than killing them, so I’m hoping this has been reconsidered.
I hope so, too. I just started the new game, so it will take some time before I'll be fighting Ethel again, but I am very curious if there are changes in patch 9.
