Love the topic and replies! My 2 cents - probably no unless infrastructure/ecosystem is built (or lets say available for regular people) for btc payments so anyone easily can pay with btc instead using visa, master etc.
You got a point here, unless the system change, fiat will never be worthless. It requires changes in financial structure to make fiat worthless and not just the price of bitcoin. Even if bitcoin reaches trillion dollar price as long as the finance system does not change, it will never make fiat worthless.