There's no guarantee, but Satoshi's paper addresses the dynamics of this - rational miners shouldn't want to undermine the validity of their own wealth. Doing things that significantly reduce the utility of the system is self-defeating even over the medium term because it'd lead people to just give up on the system in disgust and sell their coins, driving down the price. I think it's fair to say that being unable to buy basic things like food or drinks in person would reduce the utility of Bitcoin for a lot of people.