I like that you're getting multiple viewpoints and I respect what these guys are saying. What would I do? I would attend the party for the sake of my daughter (and son as he will be there) full stop. My goal would be to support my kids first and all else second.
WRT W I would absolutely have both of you go to a financial planner and put everything on the table and have that person help with a payment amount that's fair. In your case, I think it will have to get worse with W before it gets better, but having a pro help you with the finances is going to take the emotions, suspicion and wishful thinking out of the equation.
My $0.02 is that the LBS cannot "make" the WAS face the consequences of their actions. They're not suddenly going to say "oh, I did this, this was my fault I'm getting what I deserve". If they don't want to face the fact that the decision was theirs they won't.
I also think that intentionally trying to make the WAS' life worse or more uncomfortable doesn't benefit either of you. I think what you're looking for is to wish them well while at the same time focusing on yourself and leading the best life you can lead. I feel "face the consequences" comes from a place of spite and I don't think it helps you in the long run.
You asked what I would do -- that's what I would do, but remember I don't know you and don't know your wife, so the decision must be yours. I think your wife lives with the consequences of her actions every day -- she has no money, her cable was cut off, she has no help with the kids when you're not there etc etc. In many sitchs on this board the WAS is gone and involved in an affair and does not want to come back. I think those sitchs call for a more hard line approach. I believe your W DOES want to come back, but needs the finances fixed first, so I would be more motivated to act with compassion.
Accuray
Married 18, Together 20, Now Divorced M: 48, W: 50, D: 18, S: 16, D: 12 Bomb Dropped (EA, D): 7/13/11 Start Reconcile: 8/15/11 Bomb Dropped (EA, D): 5/1/2014 (Divorced) In a New Relationship: 3/2015