Sorry I thought that there was not any gift more than the exclusion and that no return was required.
There are possible civil or criminal penalties for failure to file or for evasion.
Please note that word possible - as they may or may not apply.
Late file penalty is five percent of the taxes due on the form, charged each month until the taxes are paid, but only up to 25 percent of the original tax due.
If the return was filed late because of fraud, an additional penalty of 15 percent is imposed per month. The fraud penalty cannot exceed 75 percent of the tax due.
A penalty of 20 percent is charged on underpayment of gift taxes due to an intentional undervaluation of the gift.
Penalties for tax evasion -- failing to file any form to avoid tax -- vary by situation, but usually do not exceed $100,000.
All of same possible penalties apply to estate and gift tax as are applicable to income tax.
See the table at http://www.wwwebtax.com/payments/penalties_and_interest.htm
Criminal penalties are not imposed, as a matter of policy, when the taxpayer voluntarily complies without notification from the IRS.
Most likely if the return was not filed the failure to file and failure to pay may be proposed. So, up to 50% of the tax due plus interest on the tax and the penalty could be proposed.
Worst case for voluntary compliance does not include criminal charges but the worst case would be the criminal tax penalties. For a list see http://www.taxdebthelp.com/tax-problems/tax-penalties/criminal-tax-penalties
Please ask if you need clarification.