They should be prepared in certain instances to take a fiat loss for their beliefs.
The reason is that others do the same and thus the BTC required to buy something from someone else will vary, which in turn makes people charge varying amounts of BTC in order to get the same good for the same good in the end.
Theres only 2 solutions to that:
1) Everyone has to change to only pricing things in BTC at the same time so they don't get left behind when the BTC/USD value drops
2) A slow adoption that will only lead to think being not pegged to fiat once the complete supply chain agrees on it.
That being said, a lot of prices are only shown in BTC and not in fiat already, it's just that the prices keep changing because of the BTC rate, but thats only happening on the backend. You will still only pay what the BTC price you are presented with.