No submission limit reset

Hello,
this is really a great plugin!
Only one question. My form is for a conferencem and has to have a limit of 80 submission. After that there will be no places for the conference any more, so wht do I have to do with reset submission limit.
At the moment I set it for the day after the conference (the form will be removed) but I was wondering that maybe if I’d leave it with no date, the reset will not be activated? Can you please help me?
Thanks a lot
J.