IOC revenues come largely from TV broadcast rights and licensing the Olympic name and logo on products & services (sponsors).
Remember, there's an Olympics every two years (e.g. Winter next year in Sochi, Summer two years later in Rio). There's always logistics and future arrangements to be worked out with such massive events as the Olympics. Plus the IOC has a couple of museums to maintain, the Youth Olympic Games to grow. Lastly, if employees are regularly let go, there would be a substantian brain drain. That's why, despite not knowing this for a fact, I expect most IOC employees to work full-time.
I'm an Olympics junkie.