If bitcoin looses it's usefulness as a currency the storage of value will follow. A currency without utility has no purpose. Commodities have use in manufacture, looking good, etc. Fiat has use as a medium of payment that gives it value. Bitcoin has first mover advantage but that will fade if other coins replace it as a payment method. Without that what its it? A ledger. If a coin becomes the dominant payment method there will be more demand for it and it will become valuable and thus a store of value.