I suggest: Reset the required components to default, if not found.

The required components are: dock, filemanager, panel, window manager.

My motivation / trigger situation was:
I missing the windowmanager after using mate-tweak or mintdesktop and uninstalled that tool (or the selected windowmanager).

Problem example, with missing window manager:
The selected window manager was uninstalled:

• change the window manager with an external tool ( e.g. mate-tweak or mintdesktop)
• uninstall that tool (mate-tweak) or
• uninstall the selected window-manager
• re-login
  => the Window-manager is missing.

Problem example, in detail:
Steps to reproduce:

With Mate-Tweak:

• Change the window manager in Mate-Tweak.
• After uninstall mate-tweak, the selected window manager is missing.
  Reason: Mate-tweak distribute it own marco-wrapper. ( Example: /usr/bin/marco-no-composite )

With mintdesktop:

• Change the window manager in mintdesktop (example: xfce4-wm).
• After uninstall xfce4-wm later, the selected window manager is missing.

Should be the some with uninstalled compiz.

In the case of windowmanager, an alternative fix in Mate-Tweak would be possible ( post_uninstall script Pull-Request in Mate-Tweak).