I actually thought long and hard about the whole Serena firing MC and still being able to work thing but decided against disabling it. The main reason is that I had a similar problem with this a long time ago where players were getting soft-locked after I disabled a character from appearing. Maybe it won't be an issue now, but it possibly could arise again in the future and I want to just try and remain consistent for my sanity. I think just leaving it like this is fine for now.
PS: sereevents 8 is what I want, I think.