Dramatisation, however, 1997 they still used model's to acheive effect's a lot, and cgi was used to tidy it up, rather than just complete cgi like e.g lord of the ring's, and the break up of there massive model, did actually break apparat like that. Still, ofcourse that was a model, but cameron was tryin to convey the majesty of the ship, and he wanted to get away from the night to remember type sinking. Quotin the man himself

'There's a stateleyness, to the way we preceive, the sinking of the Titanic, it was no stately'.

And with his seperation scene, I think he acheived that.