A magnetic pole reversal is estimated to take anywhere from  100 to 10,000 years. (Both ends of that estimate range being low probability) So in that sense it's not a very dramatic or a very fast process.

There is zero correlation between mass extinction and magnetic field reversals. Individual species that rely on the magnetic field for migration etc. may see significant population changes, but mass extinctions overall don't seem to be related.

The Earth's magnetic field does not disappear completely during a shift. It becomes scrambled, with multiple poles around the Earth. It is weaker, but still strong enough to do most of its job. The Earth's crust maintains some magnetism as well and this helps too. Magnetic dependent animals may well adapt to a more scrambled field, and still use it to navigate as long as it's not shifting more than a few degrees a year.

There are increased isotope levels in the rock records associated with magnetic field reversal, meaning that more cosmic rays penetrate the upper atmosphere, but overall, the Earth's atmosphere is thick enough to protect us all on its own. Incidental doses during aircraft flights will be higher, but  still not anywhere near regulatory limits. Astronauts and hardware in orbit may need more protection. However, we already have a handle on that with high orbit satellites and deep space probes. And are developing it further since we'll need it for returning to the Moon, and for manned exploration of Mars, whether the Earth's field weakens and flips, or not.

The overall radiation increase for the surface worldwide will be dwarfed by sources such as isotope release from burning coal, nuclear testing, nuclear accidents like Chernobyl and Fukushima, and just from natural sources like potassium in bananas and granite countertops.

Atmosphere and water loss to the solar wind with the Earth's reversal like on Mars as its field completely died, will not be significant.  Again, the lesser scrambled field still offers significant protection. The solar wind itself generates some of the protective magnetic field as it hits the ionosphere.

Also, the Sun appears to be entering into a Maunder minimum with few flares or sunspots.  Which also means fewer solar storms/CME's. So it could be a perfect time for a flip anyway.

So long and short of it, compass navigation might be a PITA, geese, ducks etc. might have a hard time, and space scientists will have to make some adjustments, but overall, life will go on and most won't notice,  except the Auroras might be over their house on the equator instead.

Every time a new way to measure something with more precision is discovered, it proves a catastrophe.

Satellite images ->  Ozone Hole
Global temp stations to 0.05° accuracy -> Global Warming
Remote measurement of Magnetic Field ->  Poles are moving too fast!

ALL of them are due to assumptions being made as absolutely correct since they line fit the data known at that time.   When new measurements don't fit that line, it's Our Fault, it can never be that their assumptions/models/math were incorrect.

Without a crisis, people aren't amenable to change and be controlled with new laws.   Always fear school shootings, global warming, North Korea, keep fretting about everything we have zero control over, but will be used to obtain more control over us.

It'll be cool to watch.

What this means to us, is compare a KNOWN heading via GPS to your compass reading to determine your declination change from Magnetic North.

These charts are becoming outdated faster than they thought.