Can I import photos from iPad to iMac that aren't in camera roll?
iExplorer is an app that does the trick. I just tested it, and it works.

So it's quite simple and straightforward. Launch the app, and select you iPad from the sources, there will be a Photos section, and everything should be there.

The same thing happened to me once, but I used Time Machine to backup. It must be terrifying, anyway, hope it helps!