I think TPTB will have another world war if the dollar really looks to be in trouble of failing. There is no reason why the dollar will crash but all other fiat currencies will survive. So if there are several national currency crashes that happen, which one crashes first? If the Euro were to crash the dollar would soar, and vice versa. While fiat currencies will lose "value" as they have over the decades, I don't see them actually crashing to zero, if that is even possible since they can keep printing.
There will probably be some sort of electronic gov currency created (gov style Bitcoin) and they will do away with "cash" at some point. They will use the excuse of preventing tax cheats and that they can track every "dollar" going through the system. People who hold it can still "barter" if they wish, but since it won't be legally acceptable I can see gold/silver filling that void for people who wish to avoid the e curreny.
I believe this type of environment will be a huge catalyst for silver and gold if they remove "cash" someday. Since probably 99% of the population don't hold much if any gold/silver bullion, probably won't be any confiscations again like in 1933.
One issue many stackers like myself fail to realize is that society has been conditioned to not think of gold/silver as money or valuable anymore. It would take new conditioning to re-educate the masses about PMs. So probably only stackers and very wealthy will have lots of PMs if/when this comes to pass someday.