Hi Kendra,

If this is truly a one-off deal, where there's a single page of a single document, the easiest method is probably just to find the old image from the backups, copy it over to the live installation and then drag/drop the page into the existing document.  You'll be prompted where you want to insert it (before the first page, after the last page, or as a specific page number), and after you hit OK, you'll have your old document back.

I know this is just a theoretical issue rather than an actual problem you're facing, but you may want to consider revoking the purge rights of your users.  By only allowing administrators to empty the recycle bin, you'll significantly reduce the chances of something like this happening.