We used to get similar problems on late night trains out of Leeds - we would call station security if we had concerns about anyone, they may call British Transport Police who would 'have a word' with the offending individual(s) and then declare that 'they are OK to travel and have promised to behave'
Some back-up would be nice, but given the option of refusing to take the train, which would also be the crew's trip home and wouldn't go down well with the company who would be faced with a huge fine, or the passengers (sorry, customers!!) who were behaving themselves, what choice is there, really?
Pretty much the same sort of thing as above - get them off our patch and let someone else have the problem!