Final answer:
A temporarily networked organization with replaceable firms that join and leave as needed is termed a Virtual organization, allowing adaptability and leveraging diverse skills and resources.
Step-by-step explanation:
A temporarily networked organization made up of replaceable firms that join and leave as needed is known as a Virtual organization. This organizational structure is characterized by its flexible approach to collaboration, where different firms or individual professionals come together to work on projects or to achieve a common purpose. The dynamic nature of this structure allows for companies to adapt swiftly to changing market conditions and to leverage diverse skills and resources that each member firm brings to the table.