What would you do if a store you were in suddenly closed and some how you were the only one left in there and if the workers are gone as well

They don't suddenly close they warn people .. anyway you can always call 911 or your mom to get out if they don't have an exist door that opens but that unlikely to happens. Most places have an emergency exit or can be exited from the inside somehow

I'd leave via the fire escape, if possible

Stay as still as possible so I don't trip any alarms and call 911

Get on my phone.