Well, if we use Bethel as the example, they just plow ahead as if it were any other day, because to them, it is. All operations are in full swing, although tours are usually heavy because of all the rank & file JW's who have the day off and come for the tour.
As far as private businesses run by JW's, I would think it would depend upon the nature of their business. If you have a retail operation, it probably wouldn't make sense to operate on Christmas, because nobody is out shopping on that day. On the other hand, if you run, say, a gas station or convenience store, it could certainly be business as usual.
When I was a JW working for a 'worldly' company, I used to take some ribbing, since people would say, "Hey, you don't believe in the holidays, you shouldn't take the day off!" I would usually respond that I'd be glad to work on this holiday, as well as the seven others we are closed for. But I'm not going to work eight days more than everyone else for the same money as they make, so you'll just have to give me an extra eight days off in the summer when I go on vacation. That usually shut down the topic very nicely.
Tom
"The truth was obscure, too profound and too pure; to live it you had to explode." ---Bob Dylan