In all actuality, a worse case scenario will leave you wishing your electronic devices, and cars, and livelihoods were the only things getting destroyed by the blast of unfathomable energy raining down from the sky.
The star our planet orbits, the sun 🌞, could with little to no warning at all, belch an unprecedented CME at earth that would simply strip away the atmosphere, along with all the layers of inherent protection it has historically provided, and completely change the biosphere as we know it, in dramatic fashion... Leaving whatever life that survives this event an  unrecognizable mutation.
 We, with all our science and religion, will be helpless and powerless to do anything other than die quickly.
 We might have a moment of contemplation of our impending demise, when we notice all the readings from our solar observatories go completely off the charts, and you begin to taste the sunlight ionizing the air near the planets surface... Your sunglasses no longer dark enough...
The sun can wipe this planet clean of all carbon based life forms with only a sneeze. Never take anything for granted.

I've been listening these warnings somewhat frequently since 1997. Luckily not one of them turned to be true, let's hope the same goes for this one too 😬 And +1 on both comments above, both are very good.

Even if we are told in advance, most people would be like "so" because we live in a world of conspiracy theories. What to believe and what is not worth worrying about. If electronic devices cut out, have a back up plan. It's camping time! On another level, though, most people do have some dependence on their devices and it would be crazy. Desperate people. Learning to defend what you have to survive. Water supply, food...be prepared for colder temperatures and rice and oatmeal are great fillers. Brain dump.

Very cool photo (second one). As for the stated "worst case" scenario, the actual worst case is far more than that. A big enough flare could overload the electrical grid and even electronics. It could lead to billions of dollars of damage and likely even more in lost production and trade, and months without electricity. Flipped bits caused by associated cosmic rays could lead to widespread data corruption. The effects could, and likely would, be devastating if a flare powerful enough to cause these effects were to hit, yet we've done little to protect against such an event.