Then it needs to be mailed.  As was mentioned, the IRS e-file system for 1040s shut down a few weeks ago.

And you may want to remind the taxpayer that the original due date was April 15th.  Then the IRS extended it to July 15th.  Then the taxpayer extended it to October 15th.  Then the disaster extended it to December 15th.  Did they really need to wait until this late to get their information ready?