I can add to this with info about the film, a favorite of mine. Jim survives the war in the movie, as well. After the prisoners leave the camp, they have nothing, and many die as they attempt to get somewhere that is safe. Along the way, Jim witnesses, in the distance, one of the atomic bomb blasts. Eventually, he ends up in some sort of orphanage, where his parents come, looking for him. They almost do not recognize him as he has not only grown, but is now no longer really a child in many ways. He, in turn, is so shell-shocked that he does not realize they are there. His mother, finally, realizes that the skinny young man with vacant eyes is her son.
I am not really sure what you are asking here. I am assuming that you are asking about the book here and not the film (I haven't seen the film). In the book, we know that Jim survives the entire war, therefore, he does not die at any point in the book.
We know that Jim returns to England on the ship -- the book ends with him on the ship, knowing that part of him will always be here in China.
The only scene I can think of in the book that resembles what you describe is in Chapter 30 where he pushes his box of possesions out into the river. But he clearly survives that because he walks away.
Can you clarify your question?
In the book "Empire of the Sun" Jim does survive his ordeal and returns home to England. The articles floating away is symbolic of the ending of the chapter in his life and his ordeal. In this sense it is a form of burial. He may not be able to bury the past in his memory, but the items will go to a watery grave. I recall reading an article awhile back on symbolism in the story. Ballard had stated that Jim's sins were washed away in the end. I found that to be a puzzling statement at the time. I was not sure how to interpret it, but maybe he was talking about the clothing items.
To me, I believe when Jim throws his suitcase away - he is throwing his past life away. All his immaturity is being thrown away. His previous life as a spoilt child is also being thrown away. Another reason for this is because he thinks he is going to die. Basically, he gives up.
But he does survive, throwing his suitcase in the water shows his journey of being in prison tormenting him each day that passes.