In Chapter IV ("Watchmaker") of Watchmen, during Dr. Manhattan's reflection of his life, there is a scene where he mentions his father's death and says
In 1969, I'm receiving news of my fathers death.
In 1959, he's opening a telegram from the military informing him of his son's accidental disintegration. I never correct their mistake.
So he never informed his father that he's still alive until his death (in fact this also has to imply that Dr. Manhattan's true name wasn't largely expatiated upon in the news right from the start). But I wonder why he did so. While Dr. Manhattan's increasing distancing from his own humanity and human concerns in general is a given, this seems to have been a rather gradual process and right after his rematerialization he still seemed to have much of Jon Osterman's character left, as also evident from his continued relationship with Janey. So why did Jon Osterman never reassure his father of his survival?