What will they do on a last play that needs to be reviewed

Exactly. Check the Tennessee-LSU game in Baton Rouge when Tennessee thought they had won but had 13 players on the field. It wasn't a full fledged storming, but there were lots of people on the field and it had to be cleared. Officials on the field didn't call the penalty...it was a booth review with the message coming down to the ref while people were spilling onto the field.