haha, I'm in the same position this year -- we've always spent Christmas Day with our porteno family, but this year it's only 3 of us for the 25th, so wondering the same myself for restaurants at mid-day.
The 24th from noon on it gets hard to find anything open. 25th more things are open but not everything. 31st after midnight (ie the 1st) all the clubs open up. 31st a lot of restaurants are open, Rodizio is supposed to do a good party and set meal, friends of ours go every year, do book in advance, expect to pay a few hundred pesos a head.
The 24th at night as far as I understand it is more difficult to find a restaurant. Kansas supposedly has had Christmas dinners in the past, I'm going there in a moment for a drink so if I find anything out I'll let you know.
The movie theatres aren't usually open, but it might be worth a call still, maybe the one at Abasto shopping might be open? Doubtful though as last year the malls were all closed.
New Years eve after midnight all the clubs etc open up.
To be frank, with such a large Jewish population in town I had expected that all the Chinese restaurants and the movie theatres would be open! Lol, maybe that's just a North American thing?