I'd never fly with the "neck" cord around my neck, matter of fact every tech manual I've seen instructs you not to. Post crash you've now got to worry about neck damage from the weight before they come off the mount followed quickly thereafter by the goggles coming flying back at you courtesy of the cord. What I did do was lightly tape the cord to the top of my helmet. Then when you smuck the goggles on the window/rotor brake/door frame/etc they will fall off the mount then slowly pull through the tape. This gives you lots of time to grab them before they fall and yet still gives me hope that they'll depart my helmet long before the 13g point. Last thing I want is something wrapped around me neck that can snag as I am egressing, especially underwater!
I have flown with low profile oakley style safety glasses under the nvgs, but since I don't normally fly with glasses on, the extra noise entering me ears by the arms breaking the earcup seal turned me off of them.
Tough compromise, not wanting to drop them, yet also not wanting to break your neck during a survivable crash!