You can save one mask - the halfling lady. At least it was this way in EA. I had to kill them this time around, since I somehow botched my non lethal takedown. But if the halfling lady survives, she offers you free drinks in the Elfsong inn, shoudl you come to BG, and she also gives you some interesting information about Ethel.
You can no longer do this post EA
Post EA they just become this permanent state of hostile, where they dont attack, and I am 99% certain its a bug.
In EA if you kill Ethel before you meet them, one of them is freed, the rest stay brainwashed. they need to re-implement this into the base game (or fix the bug)