One of our administrators was working on a survey page, which was completely done - he was just making a few changes. He got interrupted, and when he went back, the page was completely gone. Is there any way to recover it?

You don't have a single saved Survey page on your site... Thus unfortunately it looks like he never actually clicked the "Save" button on the Survey Maker. If you don't save your survey and then move onto another page or in some other fashion lose it, I'm afraid it's really gone. Nothing you do while constructing a survey is actually saved on the system until the Save button is pressed.

Thanks, I appreciate your reply. Looks like it's back to the drawing board ...