Created attachment 4058 my old xfce4 file I am running Debian Wheezey and at the time of losing my panel the PC was fully upto date. The PC runs 24\7 and had been up and running for 35 days. I normally logout of the desktop and then back in again on a monthly basis to refresh the setting as the setting become a little stale after a period of time, I have done this on various distro's and desktop for the past couple of years. Upon logging back into the desktop I had no panel, checking the task manager showed that the panel was running. Killing the running panel would simply start a new panel in task manager but still no panel on the desktop. I then tried a complete reboot of the PC with the same results as above. I did try selecting existing session and new session after logging in but still ended up with no panel. Task manager was still saying the panel was running. I tried a reinstall of the Debian panel package via synatics but still no panel showing on my desktop. I then tried renaming the panel folder in .config/xfce4/ and logged out and back in again but still no panel showing on the desktop. I then renamed the .config/xfce4 folder and rebooted the PC and once logged in I was presented with a new desktop complete with panel.
The xfce4-panel.xml file is indeed "corrupted", because the position property is lost. I'll add an additional check in the panel to prevent this from occurring.
The problem of loosing settings is also reported in bug #8206, make sure a position is set is applied in commit cbd8b3e.