Ukrainian grid has been targeted by russian drone and missile strikes for years and it just keeps coming back. Longest downtime (according to a quick google search) was approximately 12 hours. Complete long term blackout in a big European city is very unlikely these days.
Makes me more impressed by the Ukranians honestly! After Russia is banished they can teach the rest of Europe what resilience looks like in this area.
Organizations never prepare for a crisis until there is a crisis. It just doesn't happen. The cost of preparing for a crisis is always higher than the probability-weighted cost of the crisis itself, even if the potential impact is bankruptcy, because the probability is always so low. The only organizations that prepare for crises are those whose sole purpose is to prepare for crises.
Regulators can also impose certain preparedness obligations on organizations, like power grid black start capability (the government or system operator pays generators a monthly fee to have more expensive equipment that's capable of black-starting).
Long term as "days", yes. But all of Spain had a blackout for at least 12 hours a few weeks ago. Turin, Italy, had a 10 hours blackout yesterday.