If vrayformaya.mll is unloaded by a plug-in manager, it cannot re-load.
And Maya will become unstable if load/unload vray.
In order to delete VRay from Maya save data completely, it saves, after unloading plug-in.
Please do unload/load of the VRay plug-in without the necessity for a Maya reboot.
We can’t do this for the moment. It is on the “to do” list to look into it, but for various reasons it can’t happen quickly.
Best regards,
Vlado
Thank you for putting into a list.
hopes in the future 
In V-Ray 3.40, once it unload(s), it cannot load again.
(restart of maya is required)
We haven’t looked into this yet.
Best regards,
Vlado