Meredith,
While I agree with the request 100% and feel there should be a way to de-activate a page to take it offline, in your particular scenario I wonder why Eloqua cannot allow us to make dynamic content based on the date. I could think of plenty event use cases like yours where there are recurring events and for SEO and archiving purposes you would want to keep landing pages up for reference but not for use. Even to do something as simple as "if less than X [date]" --> insert the form into the dynamic content --> "else show alternative content [registration has ended]".