Let me ask you this, would someone who is intent on leaving the marriage want to go to a birthday party which will have my family there?
If you mean a WW, then that depends on a few things. For example, if your family knows everything, or not. What the family's attitude is toward you W. Mostly, you just never know the "whys?" behind the action of a WW. When it comes to attending family events/holidays, for some reason the WW wants to think the pretense should continue, or if she's in public, she doesn't want to be alone and will want you to sit with her or whatever. It's crazy.
Selfishness is their main motivator. She's getting something out of it, or she wouldn't do it.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!