Hi guys,
Sorry to be in your boat, glad to report a possible solution.
Fresh install of a Win 7 64 bit on a Z87 MB + Pentium G3220 CPU (using the GPU inide). When disconnecting the monitor, no image on TeamViewer. After a lot of googling, it seems to be a problem of the Intel drivers that Intel is "trying" to fix since March 2013...
1st possible solution: Remote Desktop Connection (M$ built in solution) works properly inside the network. Can possibly work for outside connections if you forward a certain port to the workstation you need to access.
2nd possible solution: If you can somehow access the resolution settings inside the workstation, you can force the GPU to manually switch to a VGA output. You are stuck at 1280 x 720 res with NO possibility to change it. The good news is that after reboot, the settings stick and you can still access through TeamViewer. I stumbled upon this and unfortunately I did't document the steps to do this. I just played around with the settings and tried to select any output...
Now, in order to do this trick, I had to install and run a trial of LogMeIn, which was able to display the initial 1024x768 screen that TeamViewer refused to do. Remote Desktop Connection is a no go since it won't allow you to access the resolution settings, it simply scales to whatever screen you are using to remote controll.
And, in the words of the immortal poet: "pics or it didn't happen"