As of now, the intent of the FHIRcast specification is to provide enough information for each app to know if it is out of sync, but not to prescribe behavior when an app falls out of sync. It is incumbent upon the application to determine the appropriate reaction to falling out of sync. This is described here: http://fhircast.org/syncconsiderations/ As we begin to see more production-grade usage of FHIRcast over the next year, we should look for potential opportunities to improve synchronization failure edge-cases – optimally without breaking backward compatibility.