Could Japan complete all five planned Yamato-class battleships in a scenario without war against the United States?
Short answerQuite possibly; avoiding the American war removes the disruption that made completion of the entire class unrealistic.
NotesCompleting five Yamato-class ships requires the program to survive long enough for later hulls to move through construction. A war against the United States diverts material, labor, and shipyard capacity while exposing the strategic weakness of further battleship investment. Without that conflict, Japan has a more plausible path to finishing the planned class. Such a decision would create an extraordinary concentration of battleship power.