Its not smart to withdraw physical cash like that, if nothing else its most at risk.  USA has laws to confiscate large amounts of cash without trial or any charges being brought, businesses have lost their cash float this way.  They may have got it back later but a small company losing 10k cash they needed to operate is pretty deadly

Other then that cash is most likely to lose its value fastest.  If you hold assets they adjust with inflation, a business is best holding resources they can utilize.   The primary use for government cash is to pay government taxes, always keep that amount ready otherwise I expect many things not just bitcoin could be a better alternative

They wont default because they cannot and survive with current administration.   The gov actively is funded by debt, even if government balances their spending to taxes it does not allow them to ignore debt obligations.  Most debt is now short term, this has been a deliberate policy since Clinton was in business and they have little room for rearrangement of the debt.   The only action really is to devalue debt worth by 'staying ahead of the curve' printing more money today to keep paying the debt from yesterday.  I forget the figure but a return to normal 5% rates would mean debt takes half the annual budget for USA and its likely similar in Japan and elsewhere and most recently Greece

tl;dr debt default will cause a currency default and many other consequences likely a breakdown in trade much like 80 years ago