The Duffer Brothers have been accused of being sensitive because they didn't remove anyone from the main cast of the show. Our heroes from Hawkins have survived a lot of supernatural disasters, like the Hopper explosion-to-Russian-prison fake out, but they haven't been living in safety.
Max was definitely the worst in the fourth season. Vecna has reduced her to a broken, empty shell, with no recollection of what happened. She is still alive because the Duffers almost took her away.
Ross Duffer said in the aftershow that it was a possibility. It was going to be that way for a while. At the end of the season, we don't know if Max is going to be okay, and we want to end it with a question. We wanted to leave it in the middle of the season.
The character's condition isn't just a "cheat" to keep her in the cast but is actually "incredibly relevant" and Matt Duffer can't really get into the details.
It doesn't seem like they've clued in on Max's fate. She hopes that she can do anything in the final season of the show. I don't know what's going on with her but I hope she's out of the hospital and out of the cast.