I wouldn't get too hung up on that.
I've had shops rebuild transmissions in old cars. Its usually a 1 or 2 day job. They dont want your car sitting down there taking up space in their lot or their bays any more than you do. They are motivated to fix it quickly and get it on out of their way to make room for the next paying customer.
The last thing they want is to park a nice customer car outside for a week and have it stolen or stripped. Then their insurance has to pay out and their policy skyrockets.
You can probably have a short conversation with them and let them reassure you. They may have a fenced lot where your car will be parked. Or you could ask them to store it indoors for the short time it'll be there.
It’s a bad joke . Good luck on your transmission.
