"It's not often mentioned but these pole reversals aren't sudden/instantaneous across the planet. They can take a few thousand years to complete."

I've actually seen that fact mentioned quite often within articles and news regarding pole flips as a reassurance to the reader.

"The magnetic field will not vanish completely, but many poles might form chaotically in different places during reversal, until it stabilizes again."

The field would not vanish completely but most of the world would lack protection from massively dangerous cosmic radiations and solar particles.