Well, lets look at some things here.

1.) Titanic was indeed designed to have her first 4 compartments entirely flooded and she wouldn't sink.

2.) Many ships have taken direct head-on hits from objects and been able to limp back to port. Take the Stockholm for example, she rammed into the Andrea Doria and the Doria sank, but Stockholm floated with a destroyed bow. Of course this was in the 1950's, and the ship was built different using modern technology, but still you get the idea. Also, another ship struck an iceberg head on in the years after Titanic's disaster, this ship didn't sink. It was a small steamer, and the story isn't widely known. I'll try to find its name and when it happened.

In conclusion I believe a direct hit to Titanic's bow would indeed have caused substantial damage to the ship, but I suspect that she would have definetly survived and would have been able to float until assistance arrived.