Why did gibbs leave ncis?

Do you know the reason that Why did Gibbs leave NCIS? If not than don't worry..

As you all know that NCIS agent Jethro Gibbs (Mark Harmon) left the team in season 19, But why?

Gibbs left NCIS at the end of season three after a terrorist attack had been successful because his superiors did not heed his warnings in time

The team is now led by Anthony DiNozzo for a short time until Gibbs' eventual return.

Gibbs explained how he felt a “sense of peace” for the first time after the death of his wife and daughter and that he was “not ready to let go.”

I know most of you might be upset but what do you think other reason could be for leaving the NCIS?

Will he ever be back again to the show? If yes than  when? I am missing him badly