Mostly yes, but IMO it's kind of over-engineered. I would do
just:
(defun workaround/describe-variable-print-bug
(original-function &rest args)
"Put temp buffer in emacs-lisp-mode before `pp-buffer'.
https://debbugs.gnu.org/39805#8";
(advice-add #'pp-buffer :before #'emacs-lisp-mode)
(unwind-protect
(apply original-function args)
(advice-remove #'pp-buffer #'emacs-lisp-mode)))
(when (= emacs-major-version 26) ;; Work around Bug#39805.
(advice-add #'describe-variable :around
#'workaround/describe-variable-print-bug))