It all completely depends on what feelings you still have for her and what feelings she still has for you and how you both feel about each other. When drink gets involved all those feelings are going to come spilling out good or bad. If you think they are more likely to be bad then just go party on your own it'll just ruin the holiday otherwise.
If you're both genuinely ok with the split then you'll be fine.
If you're both genuinely ok with the split then you'll be fine.