An interview was conducted with Shintaro Kawakubo Attack On Titan manga , where he revealed some details about the plans after the end of the series and the future of Haijime Isayama (the author of the work) as a mangaka.
To the dismay of some, Shintaro Kawakubo states that the author rules out the production of a sequel; check out the editor's words during the interview:
“There is no reason for any sequel or spin-off work. We’ve heard many requests from fans regarding this, but we regret to inform you that it’s not possible. In fact, Isayama is quite exhausted right now, so even his next serialization remains uncertain.”