It is strange that nobody gave the council that after considerable number of theme views.
I will answer my question by myself :). My problem is easily solved. Maybe it will be else useful for somebody.
I did not find any Reset or Restore button for window positions. However, if the Router window positions are lost, you can attempt to restore them by dragging and docking using Window Dragging Graphic instrument:
For details, see the PADS Router Help Topic: Customizing > Organizing Windows > Attaching Windows to the Current View.