Q:

Why didn't Michael Scott appear in the Q&A panel in the Finale episode of The Office? 

In the Finale episode of The Office, the Scranton Cultural Center hosts a public Q&A panel of the employees of Dunder Mifflin.   Most of the regular characters return for this after several months, even Kevin, who was fired, and Stanley, who had retired.   Yet no mention is made at all of Michael Scott.   Why wasn't Michael Scott invited? 
I'm also curious for an out-of-universe explanation; was Steve Carrel invited to appear one last time? 

A:

From the The Office Wiki:

"I figured the character would go back and visit everybody, but he
  wouldn't do it on camera at this point.  I think he had grown past the
  idea of being in the documentary, that was my take on it.  That
  [Michael Scott] had said goodbye to that aspect of his life, that
  that's not what was important to him.  I just thought, yeah he'd go
  back and visit, but he wouldn't want the camera crew to be documenting
  it." — Steve Carell, explaining his hesitation to return to The Office.