The general p’sak given to people who need to attend simchos, to preserve peace in the family, in which the soton is merakec beinayhem is that it’s allowed if you just stop by. To sit with mixed dancing is something I don’t think there’s any heter for.
Ask your rabbi if he’d have any trouble with you attending a simcha of neturei karta (the extreme ones, the guys who hug arafat) which will be full of israeli flag burning. Are you allowed to show up to preserve relationships with co-workers?
You’re not going to do it, but I’d love to hear what he has to say