The Ida, when a significant solar event strikes, it won't be 20 minutes. It could be 20 months.
Satellites could be destroyed beyond repair and it would take months to rebuild and relaunch them That means no long distance phone calls, no television, no internet, etc.
Electrical substations that are damaged required special transformers and other componants that are not stored as spares. There are only a few companies in the world that make them and delivery time can be several weeks or months for a single unit. In a severe solar storm, if dozens of units are damaged, it could be several months for them all to be replaced.
As noted above, these storms are relatively common, but are generally small enough to do little damage. However activity is increasing and a major storm has been expected for quite a while.
The Katrina comparison is silly. Katrina didn't cause a tenth the damage a major solar event could cause. Aside from the major systems above, home and business computers, vehicle onboard computers, basically anything with electronics could be destroyed by a major electro-magnetic pulse (EMP).
The actual measureable damage could be in the hundreds of billions of dollars.
The loss of business due to communications and transportation disruptions would be incalculable.
End of the world? No, but it could send us back to the late 1900's for quite a while.