We have been running our shorthaul fleet (including B767) with no enginers in attendance for some time now. At most airports we have an agrrement with someone to come out when called by the crew, but not all. It seems to work well. The costs go down, but the delays go up as the engineer that is called is not always available at once.
In Swden, SAS nightstops its domestic flights with no engineer on station. If a defect develops, an engineer flys up from ARN in the morning.
Many developments led to this. Loaders doing headset on pushback, the deicing crews releasing the aircraft,the refuellers controlling the refuel panel, and the cleaners converting the seats. These were all jobs that I did twenty years ago, but not any more.