Good thinking, but it's a new gearbox developed for the car, only became available last November. It may be a design weakness, and there are other people in the same boat (but not now in the same car).
I have tried, but the car rental is arranged through the AA Relay Plus system. It took them 7 days to get an automatic, it had to be brought from 97 miles away. I know, because that was the mileage on a brand new car.
The chances of getting a rental car with Cruise Control, Climate Control and Computer Display in this country are slim.
Long time ago I had a similar problem on a Ford Cortina automatic. It happened in the car park at Scratchwood services on the M1 on a business journey and much delving into the top of the gear shift established that poor electrical contact was the cause
The authorised way is to contact Vauxhall yourself if you have not already done so to establish, first, how long this situation is going to last (and where you are in the queue) and, second, what Vauxhall are going to do for you personally, if necessary by finding the name of a high up with clout
The unofficial fix that I applied was to improvise a full time completion of the electrical circuit until a new switch could be obtained, but in these days of health and safety regulations that is no doubt impossible now the car is at back at the dealer
You will likely get nothing from Vauxhall .... The replacement / courtesy car is really supplied by the dealer who would charge vauxhall under the terms of your warranty ..... it might be better to take it up with the dealership
have a small plastic cap on the console near the shift lever. If you ping the cap off with a knife you see a small slot, into which you can insert the car key (or anything else that's small enough) and push. This manually releases the park lock, and you can shift to neutral, start the sngine, and drive away.