I also thought the ending was a little odd. To be honest, the series has been slipping in these last few seasons. But at the same time, there have been some great episodes (Randy's obsession with the food network comes to mind). So I wouldn't be surprised if they hung it up, but it seems to me that Matt and Trey or Comedy Central at the very least, would make a bigger deal about it.
It has definitely been sleeping this season, like a 20-year-old car transmission that's never had any preventative maintenance.