I find the whole Navratil saga fascinating. Neither Michel nor Macelle Navratil were born French AFAIK. He was from Slovakia and she an Italian by birth. They married and settled in France and had 2 children, Michel jr and Edmond. The couple separated by 1912 with Marcelle having custody of the children. But Michel had made plans to kidnap them when they came to stay with him for Easter holidays and emigrate to America using a false identity, Louis Hoffman. The successfully got on board the Titanic and apparently told others that his wife was deceased. If the Titanic had not sunk, doubtless he would have stuck to both the name and the story, thus arriving at New York as Louis Hoffman and children. Whatever his plans had been since then, one would think that a man who planned all this so meticulously would perhaps have some sort of future arranged in the USA for his children and himself. If that was the case, it would not have been too difficult in 1912 for them to have disappeared among the teeming new arrivals, certainly out of Marcelle's reach.
About the children wanting to know about their past in later life. Had the Titanic not sunk, it would never have been famous and most of the passengers on its maiden voyage would have remained as obscure as those on board the Olympic's maiden voyage. That would have included the Navratil family and very likely Michel Sr would have told his sons the same story as he did the others, ie that their mother was dead etc. Even if Michel Jr, 3 years old at the time, had fleeting memories of his mother, that could easily have been fitted into the father's story. Therefore, it is likely that the brothers would have grown-up into two ordinary Americans without any knowledge that they had a mysterious past and so would not have bothered researching into their origins.
Somehow I feel sorry for Michel Sr. Whether his story about his wife having an affair was true or not, it looks like he really loved and cared for his children. Furthermore, in those days (and not very different these days either), courts were unfairly partial to the mother when it came to awarding custody of the children.