As I said above, the business must have INTENDED to be taxed as a S-corporation and have "Reasonable Cause" for not filing the election on time.  From you are said, the business did NOT intend to be taxed as a S-corporation until you told him about it, and I don't see any "Reasonable Cause" for not filing the election on time.
https://www.irs.gov/businesses/small-businesses-self-employed/late-election-relief