Live without fiat?
Obviously, for now, it's not possible as mass adoption of cryptocurrency is still in the early stage.
But as time proceeds day by day many will be thinking about accepting cryptocurrency as payment for their business and services by which will be the reason us to live without fiat and start living using cryptocurrency to get our needs.
I agree, and that also depends on the country or locality you're in. For example, if you live in the United States where most establishment even the small ones have card swipe machines, then it would be possible to not have any cash on you to pay for any services or goods that you would buy. However, if you live in other countries that don't have that luxury or the technological inclination, especially for old shops that are still more accustomed with using money, or small shops that would not even think of having those machines to cater to card-paying customers, then that would be impossible. Thus, it's a case to case basis.