Geologist here: no. Geomagnetic field reversed thousands of times in the Phanerozoic (last 650 My) without any relation with mass extinction events. Organisms can deal with this kind of events.
More info? According to Wikipedia, the Phanerozoic Eon has been lasting for 541 million years (I rechecked because wasn't sure what My meant at first). How would we even detect extinction events from a few million years back? Also, hundreds of millions years divided by thousands of geomagnetic field reversals sounds like very rare (considering the briefness of human existance). Also, ecosystem collapses are probably not all the same: there's gigantic explosions (a la dinosaur killer), there could be ocean acidifaction, etc.
There are a lot of good pop science books to read about the history of life on earth.
"The Ends of the World" is probably the best one. "The Rise and Fall of the Dinosaurs" is also a good one, and it doesn't focus purely on the dinosaurs as the title suggests, but about how we know how they evolved and existed.
Yes. Some technology and techniques will trickle down from defense and aerospace like it usually does. Manufacturing will be scaled up and infrastructure retrofitted. Events much more traumatic like an atmospheric EMP have been a design concern since shortly after we developed nuclear weapons. We've got well understood technology to solve any issues that come up.