Oh no! I definitely would not go. If they were just getting over a crappy cold, I'd suck it up and go, for the sake of seeing everyone for the holidays. But a stomach virus - no way! Those things are super contagious, you do not want that in household if you can help it.
There are various illnesses running rampant in our area right now, adults and kids alike are dropping like flies. We have been sick for a week here. We're grateful that we got it out of the way before Christmas, but very nervous about the possibility that our families will get sick in the next two days. Fingers crossed for good health all around!