What would happen if both Cassie and Mark went on vacation at the same time for the exact same duration and something happened on the site on their first day gone? For example, an unusual downtime. By unusual, I mean a thing that's not temporary with the server and requires manual work to get it up and running again.
Okay, but what if they had no Internet access? Where Cassie's going tomorrow, there'll be no Internet access, for example, but we still have Mark.
The entire website would start crashing down into a pile of dust and ashes and it would be wiped from history.