It sounds like when you tore the tab away, it was opened in a new window that somehow appeared offscreen. Does your host use multiple monitors? If so, with what configuration?
However when tearing away a Windows 2012 R2 tab I can no longer access it let alone merge it back. . The hidden icon box shows the VM as running however but no windows is visible.
I assume "the hidden icon box" is the icon in the system notification area?
Well just now the windows appeared in the main VMware view but it is shutdown. Puzzling (to me at least)
I don't quite understand what you mean here. Do you mean that the VM's tab suddenly reappeared in the original window and that the VM was no longer running?