Never happen. All governments start out relatively small (except for Communist states)and then grow bigger and bigger over time, until they become so large that they collapse. Hence, the need for parallel hierarchies with a moral base, or networks that take up the slack after the inevitable collapse. Christianity was one such network, that provided some kind of order after the fall of Rome.
Sure it can happen. While the federal government may collapse, we have 50 state governments with 50 state constitutions that don’t go away just because the federal government does.