probably best to NEVER delete a QR code (GHL not allow doing so) and instead just ability to make the QR code inactive (GHL setting) and therefore it could be reactivated at any time.

Example:

vCard download QR code, deactivate it, it would show some blank page or an error message like "this code has been deactivated, please try contacting us in another manner"

Then, later realizing this code was used on print pieces 3 4, reactivate it