I have managed IT departments that managed hundreds of locations and thousands of computers running Windows XP and Windows Server 2003, no cloud at all. And I went through several similar outages (similar in impact on our operations, not cause or impact on others). Our first priority was to get the critical computers that operated machinery running - we did that hours (1-2) after the problem started. Then we played around with the servers and network for few weeks - but critical stuff was operable, albeit with lesser capacity and efficiency.

And we were managing forests and waterways, not hospitals and human lives.