If you do not complete your taxes by the due date, or worse not file at all you will be facing a significant interest and tax evasion penalties. A failure to file (FTF) is addressed by the IRS at a rate of 5% a month or partial month of up to a maximum 25%. A failure to pay (FTP) is addressed with a 0.5% per month or partial month up to 25% maximum. If you are penalized for both then the FTF is reduced by the FTP penalty.
For more information when you have failed to file taxes please read this article http://ez-online-tax-filing.com//what-to-do-when-you-have-not-filed-taxes-for-many-years.html