I believe the community will need more information to provide guidance. The basic assumption is that a virtual service works on the notion of having some type of triggering event which we call a request.
Will the consumer send every request to the virtual service, and the expectation is that the virtual service will only respond if the 'Live' endpoint is unavailable?
If the consumer sends every request to the virtual service, what is the protocol used by the consumer? (i.e., HTTP, Java, JMS or MOM-based, TCP, etc.)
If the consumer does not send every request to the virtual service, what process would you expect the virtual service to perform to identify that a back-end system is unavailable; and, if the virtual service does not have a specific request, how would the virtual service know which response to send asynchronously (assume you mean this is a MOM-based architecture)?