Close the bar about 30 minutes before the end of the party.
At the designated finishing time stop the music and turn all the lights on.
Be aware that your responsibility does not cease at the front gate.
Parents should supervise the departure of the guests to avoid students congregating in the street - preferably students should only leave when transport is available. Police presence at this stage may be helpful.
Ideally find out beforehand which students are being collected by parents and which require taxis. Pre-order sufficient taxis at specified staggered times (refer 'security item 3').