Going to call BS on that one. Employers have been required to physically verify employment authorization documents (i.e., SSN or passport)
since 1986. (
https://www.uscis.gov/i-9-central/form-i-9-resources/handboo...)
Work authorization status also affects a number of things related to payroll. So it's not a trivial issue for one person, acting alone, to make up a bunch of fake employees. In order to get away with something like this in real life, there would have to have been someone else at the company in on the fraud (since, as you claim, it's a "BIG" company).
And since payroll is involved, you are looking at several federal and state felonies, which means its not the company's choice to file charges or not. Multiple state and federal agencies would pursue this even if the company did not.
This story would have been believable if you had said it was at a small startup without an HR department.