What if she had survived the iceberg, but standards were still updated as a precaution? She made it into World War One, and was a troop ship painted in Razzle Dazzle colours? What could have happened to her?
I never thought of this, but what if she had been kept in service, while her two other sisters did battle and hospital duties. But after the Britannic sunk, she was used as a hospital ship. Good point, nonetheless.
As Trevor explained, Titanic would have been fair game for any U-Boat that would have cared to have a go at her. Whether or not she would have survived is anybody's guess.
There was nothing wrong with the watertight subdivision as it was for this sort of thing. The question is whether or not the watertight doors would have been set properly for this kind of thing. For all of her modifications, the evidence suggest that they were not on the Britannic and that was her undoing.
Sounds like somebody did something right then. A merchant vessel can have a surprising amount of resistance to this sort of thing but a lot depends on the crew and what they do to save the ship as any quality of design. Bluntly, all the watertight compartmentation in the world is of zero value if it's not used properly.