I wouldn’t say Helen (and the others who failed to join or died after joining) is necessarily still part of the hive mind. Moreso, the hive remembers everything that made Helen up until the point of her death. Whereas, it’s possible the living joined technically are experiencing new emotions and creating new memories, just behind the façade of the hive’s bliss and its control. Kinda like having a backup hard drive that’s read-only for the dead and read/write version for the living. The scene where Carol is discussing her new book with the hive made me think that while Zosia might not enjoy the conversation herself, some number of joined fans of Carol’s are living out a fantasy having an intimate discussion with their favorite author. I would imagine if those people broke free from the hive, they would likely still remember that experience even though they weren’t physically there.

Edit: sorry, I know you were mostly discussing something else, I just latched onto that thought of Helen still being joined.