In the case of a costumer of mine the AWS outage manifested itself as Twilio failing to deliver SMSes. The fallback plan has been disabling the rotation of our two SMS providers and sending all messages with the remaing one. But what if the other one had something on AWS too? Or maybe both of them have something else vital on Azure, or Google Cloud, which will fail next week and stop or service. Who knows?

For small and medium sized companies it's not easy to perform an accurate due diligency.