There probably won't be anything to fall back on if it is not illegal, there just won't be anything stating it is illegal.
I have heard similar info though. Not that it is against the law to sell a vehicle which has an airbag that has been deployed but that it is illegal to disable or remove the airbag on a vehicle originally equipped with one.
Its not illegal, if that was the case vehicles that were involved in an accident that were repairable but had an airbag deploy would always be totaled. Its illegal to sell a vehicle that originally had an airbag and it was removed though (like a removable steering wheel).