This issue is fixed by the following update Description of the Outlook 2013 update: September 26, 2013
Official Response and explanation from Microsoft: Outlook 2013 Folder Pane Disappears After Installing September 2013 Public Update
One of the Outlook 2013 updates in today's Patch Tuesday release blanked the Navigation pane, as seen in this screenshot:
This is the result of mismatched outlook.exe and mso.dll file versions. This causes the minimize button in the Navigation pane to be rendered at a size that is larger than expected. This prevents the navigation pane from displaying.
It's easily fixed, either by uninstalling the problematic update (KB2817630) or by installing the August 2013 hotfix in KB 2817503.
With both the update and the hotfix installed, your Outlook version will be 15.0.4535.1004 MSO (15.0.4535.1002).
You are also likely to be missing the Repair function for Office in Add or Remove Programs. This is also the result of mismatched MSO.dll and Outlook.exe versions, however, I don't have a fix for this problem at this time.
Hotfix: Description of the Outlook 2013 hotfix package (Outlook-x-none.msp): August 13, 2013
To uninstall the update in Windows:
- Type add remove programs on the Start screen in Windows 8 or in the Start search field in Windows 7.
- Select Settings (or press the down arrow twice to select Settings, then press Enter).
- Double click on Add and Remove Programs or select it using the arrow keys and press Enter.
- Choose View Installed Updates link on the left.
- Select Update for Microsoft Office 2013 (KB2817630)... and click Uninstall.
Some users are reporting that they also need to uninstall Description of the Outlook 2013 update: August 13, 2013 (KB2817629)