score:7
Yes, you are in any case allowed to leave. The only thing between you and the outside world is the state's border and customs check and they are not in the business of enforcing airlines commercial policies. You have to fulfil all the usual Schengen rules and spending the night in a hotel (or visiting during the day) during a layover is a perfectly legitimate purpose to enter the Schengen area.
Airlines have no means of preventing you from leaving the airport and do not really care. Airport operators cannot and may not do it either. You might or might not have access to your checked luggage and you will need to have a boarding pass to re-enter.