Deleted Footage
It would have been a nice special feature on the Bluray/DVD relese but no such luck.
I'm thinking it was lost but it certainly existed up until 1978/1979 because it was used for this TV program (https://www.youtube.com/watch?v=QKzgNI7W-YI) and for SOS Titanic.
The footage shown in the TV program (6:55-7:34 and 8:44-9:20) is stunning. It shows quite a bit of misc footage including a longer take of the model sinking and without losing its fourth funnel!
There's also a different shot of the cabin being destroyed by water (more detail but less destruction); more footage of people struggling up the angled stern, in the water and in an overcrowded lifeboat and close up footage of the stern disappearing that was used in SOS Titanic.
The trailer for ANTR has a different take of the water bursting into the dining room. Like the cabin scene mentioned above the damage is less (the water hardly knocks anything over) than the one in the finished film.
And of course SOS Titanic has longer shots of the Titanic rising out of the water.
http://www.jimusnr.com/ANTRVSSOS.html