People with common sense? Governments (the institutions that get to use guns and jails and make laws) will not let their control of currency slide out from under them. Blockchains are cool and fun and applicable, but I can't see crypto-currency-as-money becoming mainstream. Even if it does the governments of the world will not adopt Bitcoin, they would make their own.

Much more likely it will be outlawed or go the way of the beanie baby. Optimistically it could remain as a financial instrument on some sort, but IMO the only reason people value btc at all is because they think it will "go mainstream". When this doesn't happen either by legislation or force the value will disappear, and with that its utility will as well.