Hi to all, just found these forums.
Anyways heres my views, consider this....

Jack tells her before dying she will survive and live on, get married have children and become an old lady that will die in her sleep.

She indeed does survive as we learn and tells "her story of events" which she amazingly had kept secret even from her husband and daughter all this time. Jack only lived in her memories as she points out there were no records of him, "there wouldnt be would their" was her quote.

After she tells her story we find the scene where she drops the necklace. The significence of this is the neckless has been her only physical bond of these memories and keeping it meant her own personal value was greater than its actual value was. "I wont let go Jack" she promised she would never forget him and their bond together.

As she reaches over shes returning it to the same ocean, his resting place, the place they made their bond. Thats were it now belongs as her time has come, her life will be fullfilled and thats were her heart lies.

The following scenes return us to her cabin where she lies in bed with the camera paning over her photos throughout her life. This brings true and concludes "Jacks belief" that she dies in her sleep, her life has ended and as the neckless perhaps falls through the ocean to we witness her soul returning to the resting place of Titanic and returning to Jack were her heart belongs.

The necklace as the engagement gift was what pressured her in wanting free, its what made her meet Jack on the upper deck, it was the only thing she had to remember him by. Its also the reason why the search expidition is at Titanic and through Jacks drawing being televised the item that brings her back and because of its bond its what would return them together. Think about it, the neckless was the link throughout the whole film and truly was the heart of the ocean.

A wonderfull story indeed...