Be worried, but don't assume this is an earth-ending event. How magnetic fields impact UV penetration is a complex process involving both physics and chemistry. One thing humans have proven very good at is modifying our atmosphere. Before we all retreat into caves we will try to boost our ozone layer. Artificial injection of ozone into the upper atmosphere is well within current technology. It isn't currently economical but would be cheaper than living like mole people.

And don't worry about nuclear power. Getting sufficient solar power won't be a problem with all those higher-energy particles getting through.