Hi Soumen,
You could get the closed docking window by this.dockingManager1.SetDockVisibility(control,true); . If you close the Docking window by clicking on the ''x'' button on the docking window, It just hides the window. Please take a look at this
test sample and let me know if this resolves your problem. Otherwise modify this sample which reproduces the issue and send it over to me.
Thanks for using syncfusion products.
Regards,
Vijay