Vehicle sales / license plates / insurance cover / Urgent, hurried very!

Hello, I have advertised my car for sale and tomorrow (Saturday in the late afternoon) an interested person comes by. Since my car is in a very good condition and because of the long journey (just under 1000km), I assume that the interested person buys the car too. The whole thing was now very short-term. But I don’t want to let the buyer drive 1000km with my license plates. On the one hand I want to keep these in order not to have to buy new ones, but much more important: The insurance cover. I don’t want to trust that nothing happens with a 1000km return trip, that the buyer also really immediately re-registers, etc. A cancellation tomorrow morning is not in question for me. Afterwards the interested person does not appear and I stand there without a car (or unnecessary costs and lots of geerenne). What can you do there? Of course, everything is now very short-term, road traffic office has only tomorrow morning. I ask for quick answer: day registration, short-term registration marks , whatever. Important: The car is registered. What possibility is there? Which data do I have to send to the interested party for this? I have already searched here in the forum and found the following: “Other possibility would be for him to drive the car with your license plate, in writing he agrees that he will re-register the car within a time limit (3 days?) and send the signs back to you. In the case (as well as for the test drive) but make a test driving contract that he will pay the costs if possible . _Accident assumes including upgrading insurance. Gives forms at the ADAC”