The server behaviour is not defined for the case where the UA A&C server is loosing its connection to the underlying system providing the condition information.

(1) Quality field
A clarification should be added that it is not the purpose of the Quality field to indicate the conneciton status of the OPC UA server to the underlying system

(2) Condition indicating the status of the underlying system
The prefered way to indicate the status of the connection to the underlying system is to provide a OffNormal condition with class System to indicate the connection status.
Options for spec enhancements:
(a) We can define a specialized condition class or condition type for this purpose
(b) We can describe the combination in a best practice appendix

(3) Appendix (best practice) for handling connection problems
We should add a new appendix that describes the strategies to inform the client about connection problems to the underlying system.
The problem is that we need to find a way to tell the client which conditions or which part of the system is not available.