Gentlemen,

Pole reversals have happened many many times historically.
We just get them on a geological time scale.

When it happens, it takes at least thousands of years to complete.
Who knows the cycles are based on so called superchrons.
Some models have it taking 50,000 years.
Anyway no one alive today needs to worry about that.


It is not a sudden phenomenon.

Worst case scenario just use declination of 180 degrees and all the regular compass math will work.

better concern what happens to the Van Allen belts and our shield against solar winds. Could really cause some problems for satellites and then with GPS down, you really need a compass too.


A lot more likely and more challenging things can happen, like earthquakes and of course astro-geo collisions which really mess things up.

Should be fun.