I had this exact issue a short while ago and I too posted an inquiry but no replies. I am using Outlook 2013, W7. I did some research and my best guess is that it revolves around MS Outlook.com. When I went logged on it too had lost all my emails. Most fortunate for me my SP had all my emails safe and secure so I was able to recover my emails. Same thing happened on my MS Surface which uses W8 and Office 2013.
If you hear of anything else I would like to hear, but for now, I can only point to Outlook.com and black magic.