TForm1 = class(TForm)
public
    { Public declarations }
    procedure CloseHandler(Sender: TObject; var Action: TCloseAction);
end;

procedure TForm1.AdvOfficePager1TabUnDock(Sender: TObject;
  APage: TAdvOfficePage);
begin
  APage.GetFloatingWindow.OnClose := CloseHandler;
end;

procedure TForm1.CloseHandler(Sender: TObject; var Action: TCloseAction);
begin
  // floating form closing here
end;