You are a little wrong over here. You meant use it as a regular currency to make day to day transaction when you said "use as fiat", right? Unfortunately, people can't yet use bitcoin as "fiat" currency. There are few issues that is stopping us from using it as a currency for making daily transaction. Look at the fees and the waiting time for one confirmation when the network is under heavy load. Do you want to pay $20 fee for buying a cup of coffee or do you want to wait for an 2 or 3 hours? I don't think you would want any. But yeah, people will eventually find solutions. So bitcoin is here to stay.