If it comes to that there probably won't be any food available to buy anyway, so we'll all starve to death on the paths leading to the illegal border crossings. That said, if someone is savvy enough to realize when it is time to move one's cash out of the country, that person is likely savvy enough to know when it is time to take themselves there as well. At least that is hopefully so because the government will not ring a bell prior to instituting currency controls or closing the border.
Newly
PS It just amazes me how many governments close their borders not to keep people out that have no right to enter, but to keep their own people in!