When the ModeShape isn't started, but its RHQ plugin is, the following exception is seen in the server log when the admin-console is accessed:

Caused by: java.lang.NullPointerException
at org.modeshape.rhq.plugin.util.ModeShapeManagementView.executeManagedOperation(ModeShapeManagementView.java:219)
at org.modeshape.rhq.plugin.EngineDiscoveryComponent.discoverResources(EngineDiscoveryComponent.java:71)
at sun.reflect.GeneratedMethodAccessor273.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.rhq.core.pc.util.DiscoveryComponentProxyFactory$ComponentInvocationThread.call(DiscoveryComponentProxyFactory.java:279)

Preferably, an error message would be logged indicated that the plugin didn't find a running ModeShape service, its cleaner.