Hi Mark,
Welcome to Microsoft Community.
I'm Hahn and I'm here to help you with your concern.
If you've sent your Surface Pro 8 for repairs, Microsoft's service options typically involve sending in your device to get quality service performed by trusted experts using certified parts. If your device is out of warranty or damaged, it may need to be replaced with a refurbished device.
However, the standard procedure does not mention providing a loaner device during the repair period. How to get service or repair for Surface - Microsoft Support
I hope this information helps! If you have any other questions, feel free to ask.
Your Sincerely
Hahn. W - MSFT | Microsoft Community Support Specialist