I’d like to note again that you will also need to reinstall the driver after an Xorg or Mesa update.
The reason is that nvidia “overwrites” some system libraries, if the corresponding packages are updated the original (non-nvidia) versions are installed again.
This will break nvidia’s OpenGL support, and is IMHO the likely reason for your problem that started this thread.
The RPM packages avoid this problem by installing the nvidia libraries to a different place.
But as I have edited zyper.conf file and changed multikernalversion to only “oldest” & “running”, i shall have no kernal update issue as my kernel will remain the same.
TBH, I don’t think this is a good idea.
And I’m not sure it will even prevent the installation of Kernel updates in the first place. I think it is only evaluated by purge-kernels.service that removes “unwanted” kernels on boot, and in that case the newer kernel will be the “running” one and not be removed either. Unless you also configured grub2 to boot a specific kernel of course.
You can avoid reinstallation on kernel modules by using dkms though, that will recompile the kernel module automatically after a kernel update.
Or use the RPM packages… 
But that’s your decision of course.
“I also remember installing nvidia the hardway back date to suse version 10.0 when nvidia installation ends & we should have to run sax cmd with some parameter to setup xorg.”… there was no issue even it was the hard way.
There normally is no need for an xorg.conf at all nowadays (since years).
Xorg will determine automatically which driver to load.
It uses a predefined list depending on the graphics card, and uses the “best” driver that is installed/can be loaded successfully.
For NVidia cards the order is nvidia->nouveau->modesetting->nv->fbdev->vesa.
i really want sax to be incorporated in opensuse 
Sax2 has been completely dropped years ago, that’s nothing to do with SUSE vs. openSUSE.
There was a replacement that created new-style xorg.conf.d snippets instead of a monolithic xorg.conf, sax3, but that never really took off.
It is still included in Leap 42.2 though.