I know Maidenhead Bahnstormer used to allow their staff take the demo bikes away for the night, weekend. How can I be so certain you might ask?
Well, I rode one of their bikes as a loan bike when mine was in for a service back in the day. This particular bike was parked next to the used stock bike, complete with the price tag clipped on to the handlebar.
When I returned that evening from work collect my bike and whilst faffing in the queue, making payments etc, the staff started to bring the bikes in from the outside, leaving only one bike out there. It was the used stock bike, but now without the price tag on it. One of the techs took it home with him. So yes, Staff were allowed to take dealership demo or used bikes for their own pleasure.
Perhaps yours got taken by a "senior" member of staff, who has the "supreme authority" and no one can say shit about it.
Just a thought.
Edited to add:
Just remembered...
Dean (the main fellow) at Bahnstormer, even shown me a photograph of him away on a GS in Italy, that I have purchased as a used bike from them, just a few months later. It was registered to them as a Demo, then somebody purchased it, and PXed it against something else a fairly short while later. So I was the third owner on the logbook, between September 2014 and late March 2016.