Having the group fail Pierce's test, though, is not unexpected. They forgive him when he saves the day and invite him to rejoin the group, despite kicking him out when he betrayed them in part one. It's what it is expected from an ensemble comedy. Everyone will come back together at the end of the day, and peace and balance will be restored. That is not what happens, though, as Pierce tells the group he's done with them.
What does this mean? Is Chevy Chase leaving the series? Will Pierce be an all-out villain next year, bent on destroying the study group? He already has formed an alternative study group before, which failed, and people don't like him, so it's unlikely he'll have much help. However, with Chang (Ken Jeong) also struggling to find a place on the series, perhaps it's time the two team up for awhile and spend some time together. Whatever happens, the whole dynamic has changed. While it feels good to get the poison out of the library, it's also sad.
How likely is it that Pierce will never return to the study group? Most series would not mess with their proven formula. But Community has shown a willingness to take risks over and over again, as evidenced be their oh so many special episodes just this past year (Halloween zombie attack, Christmas claymation adventure, all-original clip show, etc.) If any sitcom would drastically alter a main character to move in a new direction, it would be Community.
It seems Senor Chang will never officially be part of the group. They haven't really been comfortable with him, and it's because they know he is not loyal. In the first part, Chang switches from group to group whenever he thinks it improves his chances of staying in the game. Study Group does not roll that way. Unless Chang changes fundamentally, he cannot truly be one of them.