(require 'tile)
(setq tile-two-windows (tile-split-n-tall 2))
(defun delete-other-windows-or-split ()
  (interactive)
  (if (one-window-p)
      (tile :strategy tile-two-windows)
    (delete-other-windows)))
(global-set-key (kbd "C-x 1") 'delete-other-windows-or-split)