a currency doesn't go "bust" suddenly, they just print out more money under the guise of some .......( insertion place for the politicians motivation)reason. 
That scenario is exactly what I would call "bust". And it has already begun. It just hasn't played out to the end-game yet.
My views are consistent with the expectations voiced by Ambrose Evans-Pritchard recently (in the Telegraph), that "a world awash with excess capacity cannot withstand a fully-fledged dollar tightening shock. The effects will ricochet back into the US eventually, but that could be a long time hence, and this in a sense is the problem for asset markets."
...reliable ( to certain extent) because it has a government backing the currency ( which is saying every resident of said country is backing that coin/currency)...
As the U.S. wealth distribution shifts to Gini extremes, the ability of the population to effectively back the USD declines with their declining share of tax burden. Those who are able (the few wealthy) are disinclined to expend their wealth backing the USD. They rotate offshore first. They will avoid the tax burden, so they cannot be expected to support the currency.
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Still the elites, banks etc are in charge and do you really think they give everything up without a fight?
Of course not. They are first into the lifeboats. Death by drowning is reserved for steerage class passengers. Heck, that's what lifeboats are *for*.