> How does a medium-sized SME were all the payrolls depends on Sara and her USB stick do if, literally, their servers do catch fire.

Like every job, we overestimate our importance.

What do they do? They pay everyone the same as last month as a temporary measure, ask you to talk to your manager if your pay should be more this month, warn everyone that they're going to recalculate the payroll and adjust any differences next month. Then they calculate everyone's pay from the inputs, which really isn't such a hard problem when the alternative is failure. Maybe they pay some fancy consultants or an SAAS provider for a few months. Maybe they have to cut a few corners. Maybe they even get fined by their state's DoL. Life goes on.