I do remember on a Monarch flight to Malaga from Man circa 20 years ago where about 12-15 on a stag do.
Flight circa 60% full. Group spread all round close to back of plane.
Guy in charge said to passengers around they on stag, apologised well in advance for behaviour and suggested that if they wanted to swap with others on stag so they all in one place.
Everybody did including gorgeous BA trainer that sat and chatted to me all flight and never asked for her number
The stag party drank and a bit loud / leery but even FA said they ok and had 2 who were in control.
Spoke to one of stag group waiting for bags and said thanks, he looked on being in control for a couple of hours as better than all getting chucked off flight. He claimed the deal all agreed was 2 in charge were in charge and ensured they all got there.
Now airlines flying stag / hens the option I like is find someone in charge and make it clear before flight takes off that will deny all boarding or cancel all if have to divert.
On this specific flight I think 48 hours held in custody and then released is a good option as they miss everything.
FR is not only one that has issues with Stag/Hens as everybody has.