It is really not going to be worthless and not just ten times but millions of people are preferring to use fiat. Because that is all set that fiat is one of the currency that has been using by so many countries throughout the world. And bitcoin is still new many are going to have their doubts with it and will still choose fiat over whatever its price.
Yeah i think whatever the price of bitcoin is, it still would rely on fiat conversion. You can't really use btc as it is in mainstream market today as most transactions are still through fiat. So i don't think the price of bitcoin, whether it goes up or crashes, would have a significant effect on fiat currency