Delta has a metadata layer where the data files corresponding to each state of the table are being referenced. What happens in the unlikely situation when a user unintentionally deletes a data file referenced from the metadata table. Is the table (or the history of the table following the addition in the metadata of physically deleted file) considered corrupt and can't be repaired anymore?

It's corrupted and you may be able to repair it. Depends on if you can recover the files. Only the versions of the table that reference that file will be invalid