helm 標準の helm-kill-selection-and-quit は、 heml を終了した時にバッファ名を kill-ring に保存するので heml-mode が終了してしまう。
helm-kill-selection は バッファを kill-ring に保存した後も helm-mode を継続する。

;; 選択しているアイテムのバッファ名を kill-ring に保存
(defun helm-kill-selection (arg)
  "Store display value of current selection to kill ring"
  (interactive "P")
  (with-helm-alive-p
    (let ((src (helm-get-current-source)) helm-saved-selection helm-saved-selection-name)
      ;; (helm-log-run-hook 'helm-select-action-hook)
      (setq helm-saved-selection (helm-get-selection nil nil src))
      (case (type-of helm-saved-selection)
        ('buffer
         (setq helm-saved-selection-name (buffer-name helm-saved-selection)))
        (t
         (setq helm-saved-selection-name helm-saved-selection)))
      (kill-new helm-saved-selection-name)
      (message (format "Saved to kill-ring: %s" helm-saved-selection-name))
      )))
(put 'helm-kill-selection 'helm-only t)

;; キーバインド
;; (define-key helm-map "\C-c\C-k"   'helm-kill-selection-and-quit)
(define-key helm-map "\C-c\C-k"   'helm-kill-selection)