"Control theory" isn't a term I'm particularly familiar with, but I can at least say that this isn't correct. Cybernetics didn't exist in any unified fashion prior to Wiener writing the book on it in 1948, and it didn't last more than a couple decades afterwards before being laundered piecemeal into mathematics, technical subfields, philosophy/anthropology, and a couple other things of varying interest (Stafford Beer's "Management Cybernetics" is probably the most notable example).
There was a particular schelling point in the '40s surrounding Wiener (and Shannon, Von Neumann, etc) and the Macy Conferences who were searching for an interdisciplinary umbrella, and found it in Cybernetics. It began as something decidedly "para-academic" and never really grew beyond that. The scope of Cybernetics was — and probably is — too broad to fit into a rigid departmental system. Instead of thinking of it as "going" away, it is probably more accurate to say that it never really arrived.
There was a particular schelling point in the '40s surrounding Wiener (and Shannon, Von Neumann, etc) and the Macy Conferences who were searching for an interdisciplinary umbrella, and found it in Cybernetics. It began as something decidedly "para-academic" and never really grew beyond that. The scope of Cybernetics was — and probably is — too broad to fit into a rigid departmental system. Instead of thinking of it as "going" away, it is probably more accurate to say that it never really arrived.