NO, NO, NO.
Seriously.
If they had closed campus for the day at 7:15 AM, word would have travelled.
Those kids who DID arrive for 9 AM classes would have found a locked door and returned to their car.
When the A-hole showed up at 9:30 to begin capping people, it would have been slim pickings. he could have walked to the dorms, and tried getting kids to open their doors (however by then, the announcement system should have been telling them for 2 hours that a double-murder had occurred and they had no idea where the shooter is - so don't answer your door. Or he could have stood in the parking lot, and taken potshots at cars entering - which would have got him run over, arrested, or fired back at, pretty quickly.
Either way, it is ABSOLUTELY true that a closed engineering building would have resulted in those 60 people not being trapped in classrooms. The numbers should have fallen as a result.