You don't need a DoS attack under the assumptions of this project. It's already assumed that you control ~80% of hash rate, so you execute a 51% attack that mass double-spends coins and destroy all confidence in the integrity of the currency. Poof, nobody uses it. Note that China already controls ~65% of Bitcoin hash rate, so if they wanted to execute this right now, they probably could. That they haven't is one reas…
How would a hyperinflation on the US dollar cause civilization to stop? In any case, crypto trading since 2017 has been nothing but people buying and selling imaginary ticker symbols on unregulated exchanges. For example, XVG and ETC has been subject to successful 51% attacks more than once and every time the price was hardly affected. And each time the "solution" to deep chain reorg involved the exchanges freezing a…
The dollar is the value used to denominate world debt via the IMF. It's also (partially related to this fact) the "mattress currency" of a lot of nations... Nations hoard US dollars to back-stop their own economies, since if their currency starts to tank, they can use dollars to pay their international debts.
A worthless US dollar would have wide-ranging international currency disruption.