Advanced server software is constantly checking critical services on the web server and can automatically restart them if there's any trouble brewing. You'd never even know if we didn't tell you, so we will: This has happened 4 times in the past two years. No downtime.
We use two external services to monitor our servers. Minute by minute they mimic a web visitor, and alert us to any problems. While this is extremely rare, we have confidence knowing we'll find out about any trouble before you do, as alerts are sent direct to our technicians mobile who is qualified to take both evasive and corrective action.