If this service was cancelled what would FGW▸ have done?
Provided alternative transport, i.e. a bus or taxis. It's all covered in the conditions of carriage.
And on the alcohol point, it doesn't do a lot of good banning alcohol on the service if people are already well oiled before they get on board - like you said, they only travelled from bath to Bristol. That must have taken all of 15 minutes. Not even I could put away enough booze to do that much damage in 15 minutes.