I suspect we will continue to do what we currently do: differentiate between magnetic north and "true" north, by applying a local correction, as is already required for navigation with a compass.
Depends on your definition of minor. As is, you cannot use magnetic north to navigate, alone, in the east and west of North America. It's 20 degrees off in Oregon, and nearly 40 in northern Alaska. This is something you quickly learn in boy scouts, by getting lost in the woods, if you live on the coast.
But, considering it takes 1,000 to 10,000 years to flip, nobody involved in this will be surprised when they look at their compass. They'll have remembered their local correction from when they were children.
