Yes, if you were an S-Corp, recognized by the IRS and had that S-Corp election revoked, then you would need to file a Part-Year final 1120-S Tax Return. It will have all the expenses and income of the S-Corp through revocation.
You would then need to file the remaining part of the year as a sole proprietor on your Schedule C of your Federal Income Tax Return.
*IF* the LLC had made the election to be taxed as corporation, and if it completely ended in September, that tax return was due December 15th.
Yes, if you were an S-Corp, recognized by the IRS and had that S-Corp election revoked, then you would need to file a Part-Year final 1120-S Tax Return. It will have all the expenses and income of the S-Corp through revocation.
You would then need to file the remaining part of the year as a sole proprietor on your Schedule C of your Federal Income Tax Return.