Okay, I have good news. You can force an exit from Unity mode entirely from within the guest. If you do this from inside the guest OS, while you're in Unity mode, you will cause Unity mode to stop:
C:\>"c:\Program Files\VMware\VMware Tools\vmtoolsd.exe" --name=vmusr --kill
This will return the desktop background to what it was before Unity mode and should cause the task bar to show again. When you later return to your OS X desktop, you should see Fusion telling you that the VM is unable to run Unity. You might be able to get Unity to restart automatically by running this command from inside the guest (assuming Fusion is waiting to be able to enter Unity):
C:\>"c:\Program Files\VMware\VMware Tools\vmtoolsd.exe" --name=vmusr
... but I'm not 100% sure. To be safe, it would be best to restart the guest VM when you come back to your OS X host before trying to go into Unity again.
Does this help?