Boot the system in safe mode (link below).  If the nVidia GPU shows in the device manager, you have a corrupt driver installation and will either need to reload Windows or remove and reinstall all the video drivers (starting with the Intel driver).

If you do not see the nVidia GPU in safe mode, it has failed, in which case you'll either need to run the system as is (Intel only) or replace the system board.

Safe mode access:

https://support.microsoft.com/en-us/windows/start-your-pc-in-safe-mode-in-windows-10-92c27cff-db89-8644-1ce4-b3e5e56fe234

I know it may sound weird but today it all started showing up and nvidea control panel got installed from windows store also. I dunno what's going on. Can anyone explain.

@sanatpratik​ I am having the exact same problem as yours, at first the dgpu (MX450) went away then reappear and after some time it disappear again and after that it never reappeared and gone like it never existed, I also tried all the things you mentioned above, after that I saw your article can you help me please? 

I checked the dgpu in bios also and there is nothing written in discrete gpu section and the PCIe bus 01 is showing empty, previously the dgpu was on PCIe bus 1.