According to his Linkedln page, Jimmy Zielinski (who was on the team that created the original Call of Duty Zombies) left Treyarch Studios back in December 2014.
Zielinski was on the team that created the original Nazi Zombies and responsible for creating “numerous high quality Zombie experiences spanning World at War, Black Ops and Black Ops II,” according to his Linkedln page. Zielinski has not stated as to why he left Treyarch.
The current Director and Sr. Executive Producer of Zombies is Jason Blundell, who worked on Mob of the Dead and Origins Zombies experiences. He’s also working on the campaign for Call of Duty: Black Ops 3. Blundell will take the stage at Comic-Con on July 9th to reveal Black Ops 3’s Zombies mode.