The current (9th) season is the last season for the show. It starts Jan 10th and when it ends that'll be it. What really hurt the show is when some of the writers left (around when Sabre took over).
The guy that plays Toby (HR guy) was actually one of the main writers for the show, he stopped writing to work on the spin off, The Farm.
And yes, it absolutely sucked when Michael left. You can always tell when an actor is really, genuinely emotional and in the episode where he actually leaves you can really tell. Especially the cut where he's like "Yep, this is gonna hurt like a mother
er". I did not like any of the bosses after he left up until Andy took over, then it was ok again.