As someone that liked Pierce back in seasons 1 and 2, I feel like his character doesn't have a purpose on the show anymore. His character was defined early on as someone that's so obnoxious and offensive that he ends up pushing all his friends away, and that's what happened in season 2 when he became something of a villain. His arc came to a conclusion at the end of season 2 when he left the study group, but rather than leaving it there they neutered the character so that the status quo could be maintained. I think it would have made more sense if Chang replaced Pierce in the study group and Pierce became the new external force that resented/idealised the group. But if he's to leave the show instead, so be it, he's not much of a loss anymore.