No, you don't have to write off your helmet when a vizor attachment fails. Nor is continuing to ride without a breath deflector or nose cap a necessity.
Just about all LS2 parts which can get lost, can break or wear and tear can be found here. Except the helmet shell. If that breaks, we really need to push for a new helmet.
The correct model of helmet is always listed in the product description, because it goes without saying that you shouldn't tinker with combinations yourself.
The LS2 vizors are bundled in a separate product group.
Tip from the RAD-house
A helmet is designed and made to provide 100% protection once. One time. Make sure that one time is not in your garage or at the kitchen table and keep your helmet safely on a helmet donut while you're working on it.