I'd be pissed off with the late changes to what is assumed to be a normal Christmas Eve. Christmas Eve is part of the main event here.. the conjuring of magic once the kids are in bed (as in Santa, not david copperfieldesque sex), watching a movie together, generally enjoying Christmas.
As that's the done thing in our house, if DH (or myself) announced we were off out, to get drunk, then I (or he) would be pissed off. So Foxsbrush YANBU. If that's the case.
If its the case that actually there is no agreed 'eve' family tradition, because neither of you have ever discussed/planned it, then YABU to assume it would just happen all by itself.
Even though my DH and I fortunately want the same sort of Christmas, we always always talk it through, because he's shit at days of the week (he only just realised today is Christmas Eve EVE, not Christmas Eve, and has gone out for a drink with his mates rather than turn them down lol) and I'm shoite at having things sprung on me.
Christmas eve for us is less about the kids (apart from trying to settle them, telling them stories ad infinitum and general christmassey exciutement) and more about DH and I creating a magical Christmas, and for that you don't need to be stone cold sober (perish the thought) but you do need to be present at least, and not rolling drunk. So for that, and that alone YANBU.