Well I know of two people who have dropped for sure.  

I am reasonably confident that Apoalo and Eyeris are still around.  Probably Roze as well, and add you and me to that list and it's still sizable.  

On that note, if your character is not already seated, get them to their House table because my next post will have Professor Black opening.  Might be a brand new, original Sorting Hat Song™ if I can get a satisfactory one written.