https://screenrant.com/why-paget-brewster-emily-left-criminal-minds/

Criminal Minds said goodbye to Paget Brewster's Emily Prentiss on two occasions, and she left and returned to the BAU for different reasons.

Criminal Minds: How Paget Brewster’s Emily Prentiss Died, Left & Took Over the Show (https://www.cbr.com/criminal-minds-prentiss-death-return/)

Emily Prentiss became one of the most beloved and long-term Criminal Minds cast members, despite her late start and rocky treatment by the studio.