What happens to Workday integrations during service updates?

tl;dr: It mostly "just works"

This Community Post explaining it, Concept: Integration Schedules and Weekly Service Updates

A bit more:

The tenant goes into "service update mode" 30 minutes before the update.

If the integration starts before the tenant enters "service update mode" and ends in the 30-minute window before the update -> No impact.

If the integration starts before the tenant enters "service update mode" and doesn't complete before the Weekly Service Update beings -> Workday will restart the integration when the weekly service update completes. However... There are a number of scenarios listed on the Community post where Workday won't restart the integration.

If the integration is scheduled to start after the tenant enters the "service update mode" -> The integration won't start at it's scheduled time, it starts after the Weekly Service Update.