Can Get Menu close the day for me if my staff forget?

Yes. Under Settings → The POS, Close the day automatically, tick it and set a time after your closing time on your restaurant's clock. If nobody closed the day by then, Get Menu closes it: nobody counted the cash, so the report says NOT COUNTED and everything in the drawer is carried to the next shift, where the opening count is checked against it. Open tables and unpaid orders move to the next shift, and the day report and the WhatsApp summary go as after any close. The POS and the counter tab in the docs covers the automatic close.