Final answer:
The correct term for team members ready to augment the company in extreme circumstances is 'On call'. They provide expertise and support when urgently needed, although they are not on the regular work schedule.
Step-by-step explanation:
The term that refers to team members who are available to augment the company in extreme circumstances, when additional expertise and support are required, is On call. This means that these team members are not on the regular schedule but can be called upon when their special skills or additional manpower is necessary, usually in urgent or unforeseen situations. The options provided in the question are various terms related to work status and availability, but on-call is the term specifically associated with being ready to work if needed outside normal working hours.