In the Live Event production flow, encoder and MS Stream Live Event organization are loosely-coupled, which is a good thing !! You can setup your Live Event, and then an encoder to stream the production to the Live Event egress point. In Stream the organizer has the control when to actually start the event: so not start yet when encoder is not connected yet, or is facing an issue.
When during the event an issue occurs with the encoder, of when you would need to switch; the input on the egress point will temporary be lost. The effect in Stream, and towards the event audience is now a technical error. This can be more elegant handled in case in Stream the organizer has the option to temporary inject an own customized 'disturbance' page. This could also be used when you want to switch in the same Live Event from locations: starting with presenting from Amsterdam (encoder 1), then switch over to presentation in Redmond (encoder 2). In the streamed signal, then a message could be displayed "Switching over to Redmond", which gives a much more professional impression as temporary displaying the technical error on lost of input on the egress.