I'm torn hopeful. On one hand, you should absolutely be able to go to something as simple as this without having this stress hanging over it.
On the other, it's your daughter we're talking about. When is the last time she needed to be picked up during his custody days?
Both he AND the GF have been flipping out unpredictably lately so for me, I think it would come down to whether I thought he/they were more likely to go off half-cocked THIS weekend. Is he more likely to binge a lot between now & then or to try to "be good" until he gets settled in with the new job? Does having all this time off before starting work for him or against him? (I could easily see him binging right up until Sunday?)
Does she ever play a part in his binges, unknowingly? (I don't want this to sound insulting to everyone here - but I know that *I* was guilty of this before I realized how I was creating drama because *I* didn't know how to act in absence of it after so long of that being part of My Normal.)
No matter what you do, you're having to try to predict the future. I think I would aim for what would leave me feeling the least resentful in the long run, if even THAT can be predicted!