It depends on how the software works if you file after the deadline. The eFile system is left open for 5 days in case an eFile is rejected, but I do not know if you can successfully do an original eFile after midnight on the October 16. Others have asked that question and I have not seen an answer saying that the late eFile will work.
I think you can just wait a few days and then go to www.irs.gov/refunds and see if it is accepted. If it will not go through you will have to print and mail your return.
