IMO Bonfire Night, if promised, should be attended.
Punishment is all very well and only you can judge how deserved but Bonfire Night only happens once a year. That is a 12 month looooooooooooooooooong punishment, making him wait 'till next year for another chance. Could you not compromise by taking him but making it plain that he COULD have missed it because of his behaviour.
To be honest this is why I favour corporal punishment at school. Justice (or injustice) is immediate. I simply do not like this "we'll report you to your parents for them to take action" routine. Makes me the bad guy when in fact the child has usually done nothing that I didn't do at school myself. For the same reason neither wife has been permitted to use the "wait 'til your father gets home" threat. I will not punish for something that happened in my absence. If I catch them then they get what's coming but I'm damned if anyone else is going to tell me to punish a child on their behalf.
Sorry ~ butt out Snoopy ..... 'snot your business.