I've just created the missing plugin to revert V-Ray materials back to internal.
For now it's target is only to prepare file export via .fbx and similar, since this operation didn't support plugin material.
here link to description:
and here direct link to Gumroad:
it has a reasonable price of 10$ (or more
Any suggestion will be really appreciated.
Thanks @kosmos3d for the contribution and making the whole community aware of it.