Originally Posted by PHLJJS

Usually, TSA sticks around until the last flight departs, so the checkpoint would stay open at least until boarding for the flight is finished. It sounds like they weren't expecting too many people to come through that late and starting shutting down the equipment a little early.
If you showed up late, the checkpoint was closed and there was no one around to screen you, then I'm guessing you would be denied boarding. I have heard of flights getting diverted to small airports after closing and for whatever reason the airport/ airline people let passengers deplane and exit the airport or sterile area, requiring those passengers to be re-screened. The story was that the airport got in touch with a TSA manager and they got some TSOs to come back to the airport and screened the flight.