I agree. Shame that your son feels that it is your job to stop his father drinking or making an ass of himself.
That said, I don't see how you have any duty to mention it to your hubby. Surely this is the kind of thing he ought to know or remember and if he finds out after the event, then that's just a consequence of his drinking. He's an adult, isn't he? Then he should be able to organise his own social diary and committments.
You enjoy yourself, hon, and give your GS a big SR hug from all of us.