My favorite MA is gone as well. I adore her so much because she's the person who got me into makeup (and MAC of course) and got me on the right foot. I would only see her occasinonally over the course of a year and noticed that I hadn't seen her at all this year. So about a month ago I asked the MA who was helping me what happened to her and she said "Uhh ... she doesn't work here anymore" like she really didn't want to talk about it. I asked "Why?" and she said "Hmmm, I really don't know! I don't talk to her!" and changed the subject to lipstick.
She never really seemed happy though. She was still nice and did great makeup, but she just didn't seem happy at the job.