When we are thinking about a realistic scenario then there wont be a time when there is no fiat money at all, we might see the entire fiat currency we use know use as digital currency but never expect anything more than that, bitcoin is not invented to replace the fiat currency and the financial crises in 2008 is not the first crises and will not be the last one, it is a cycle and we will see those kind of crises in the future too, if there is a centralized crises then the decentralized market will boom without a doubt.