Here's why Agent Percy is no longer part of the team at NCIS: New Orleans. NCIS stands for Naval Criminal Investigative Service, and the team was first introduced during an episode of JAG. The concept and characters, including Gibbs and DiNozzo, proved popular enough to launch a solo NCIS series, which attracted a major following. The show has been running since 2003 and its seventh season will premiere in September 2019. Fans are especially excited for the coming season since it marks the return of a certain fan-favorite character.
The success of the show led to other spinoffs, with the first being NCIS: Los Angeles, starring LL Cool J and Chris O'Donnell (Batman & Robin). That series has run for eleven seasons thus far, and the franchise branched out once again with NCIS: New Orleans. Main characters Dwayne Cassius Pride (Scott Bakula, Quantum Leap) and Christopher LaSalle (Lucas Black) were introduced in a backdoor pilot episode of NCIS season 11. Like its predecessors, the show has strong ratings and will return for season 6 in late 2019.
NCIS: New Orleans follows agents stationed in the Big Easy, led by Bakula's Pride. His agents include LaSalle, Tammy Gregorio, and Meredith Brody. Sonja Percy (Shalita Grant, Santa Clarita Diet) is a former ATF agent who was a recurring character during season one but later joined the team in season two. She and Pride had a tricky relationship, however, and he feared her occasional undercover activities for the ATF could endanger his team. She and LaSelle also developed something of a "Will they, won't they?" relationship.
Shalita Grant decided to depart NCIS: New Orleans during season 4, with the series planting the seeds for her departure by mentioning an interview with the FBI. Episode 19 "High Stakes" was Sonja Percy's final episode to date, which involved an undercover op at a poker game. Percy hands in her badge after the operation ends dramatically - a move Pride supports - and she accepts a position in the FBI instead.
There's scope for Sonja Percy to return to NCIS: New Orleans in the future, though there doesn't appear to be any plans for the character reappearing. She added an interesting dynamic to the team, with Pride never entirely trusting her - though they had respect for one another - and she and LaSalle having an unrequited attraction. The series has taken plenty of dramatic turns since the character left, however, since life in the NCIS office is rarely dull.